43 TAC §§25.20, 25.23, 25.24
The Texas Department of Transportation adopts amendments
to §25.20, concerning definitions, §25.23, concerning speed zone
studies, and §25.24, concerning speed zone approval. Section 25.23 is
adopted with changes to the proposed text as published in the March 10, 2000,
issue of the
Texas Register
(25 TexReg 2018).
Sections 25.20 and 25.24 are adopted without changes and will not be republished.
EXPLANATION OF ADOPTED AMENDMENTS
Transportation Code, §203.002, authorizes the Texas Transportation
Commission to lay out, maintain, construct, and operate a modern state highway
system.
Transportation Code, §545.353, authorizes the Texas Transportation
Commission to determine a reasonable and safe prima facie speed limit for
portions of the designated state highway system. Section 545.353 also requires
the Texas Transportation Commission to adopt procedures that will be used
to determine speed limits on the state highway system.
Pursuant to these statutory powers, the commission determines that a prima
facie speed limit may be determined to be unreasonable if lowering that limit
will contribute to the protection of the public health or help prevent the
imposition of sanctions or restrictions on the use of federal transportation
funds. The department, therefore, is modifying the existing rules for establishing
speed zones. The amendments will allow speed reductions on the state highway
system in order to assist areas in achieving and maintaining federal air quality
standards. These speed restrictions are referred to as environmental speed
limits (ESLs) in the proposed revision.
The federal Clean Air Act and subsequent amendments require areas to meet
federal National Ambient Air Quality Standards (NAAQS) determined to provide
an adequate margin of safety to protect the public health. These standards
limit the amount of certain pollutants that cause or contribute to air pollution
that an area may have present in the atmosphere in that region (such as sulfur
oxides, ozone, particulate matter
10
, carbon
monoxide, nitrogen oxides, and lead). Failure to meet these specified air
quality standards may result in an area being designated as "nonattainment."
Texas currently has four areas in nonattainment for air quality: Houston-Galveston,
Dallas-Fort Worth, Beaumont-Port Arthur, and El Paso. Federal regulations
require each nonattainment area to have an approved air quality plan (referred
to as the State Implementation Plan) for attaining and maintaining the NAAQS.
Nonattainment areas are also required to meet transportation conformity requirements,
which ensure that on-road vehicular emissions do not exceed levels that will
allow areas to attain and maintain the NAAQS. Failure of a nonattainment area
to have an approved SIP or demonstrate transportation conformity can result
in the imposition of federal sanctions or restrictions for the area in regards
to the design, construction, maintenance, and operation of transportation
facilities.
The department is amending the existing rules regarding the establishment
of speed zones on portions of the state highway system. These revisions will
allow reductions in the existing regulatory speed limit on portions of the
state highway system for previously mentioned environmental considerations.
A reduction in vehicle speeds can help reduce the production and presence
of ground level ozone. Currently, the Dallas-Fort Worth and Houston areas
have proposed future reductions in speed limits as part of their State Implementation
Plans (SIP) for air quality.
The rules also allow the Texas Natural Resource Conservation Commission
(TNRCC) to request such speed reductions for areas as necessary to attain
and maintain the NAAQS or meet transportation conformity requirements. Transportation
conformity refers to the demonstration that a nonattainment area must make
under federal regulation that emissions from on-road mobile sources (such
as motor vehicles) and transportation projects conform to the area's air quality
plan.
Under these amendments, the department will accept and evaluate requests
from the TNRCC for reductions in existing speed limits on the state highway
system. Reductions of up to 15 miles per hour of existing regulatory speeds
will be considered for controlled access and non-controlled access roadways
for environmental considerations. The minimum speed limit possible under this
amendment for a controlled access roadway will be 55 miles per hour and 45
miles per hour for a non-controlled access roadway.
Such a speed reduction will be part of the TNRCC's SIP for air quality
or an area's transportation conformity demonstration. The TNRCC will make
such a request to the Texas Transportation Commission through the department's
Traffic Operations Division. The commission will then make the final determination
for approval or denial of the request. Upon approval of an ESL, the department
will be responsible for all costs associated with the removal of all existing
signs and installation and maintenance of the new speed limit signs on the
state highway system.
The amendments to §25.20 add new terms used in the amended sections
such as "TNRCC," "NAAQS," "nonattainment area counties or area," "State Implementation
Plan," "control measure," "transportation conformity," and "emissions reduction
measure."
Section 25.23 is amended by adding new subsection (f) to allow the creation
of environmental speed limits (ESL). This section also describes the process
by which the TNRCC may request an ESL from the department for a portion of
the designated state highway system.
Under new subsection (f), TNRCC will be responsible for all studies necessary
for the creation of an ESL. Any proposed ESL will have to be part of the TNRCC's
environmental/air quality study and modeling considerations. A proposed ESL
must be either contained in the area's SIP as a control measure or fulfill
transportation conformity requirements. The TNRCC is further responsible for
including a description of all locations for proposed ESL on the state highway
system. Since the TNRCC is the state agency responsible for developing a State
Implementation Plan for air quality, the department believes it is appropriate
for the TNRCC to develop all supporting documentation related to a proposed
ESL. This subsection also requires the TNRCC to notify the commission, through
the Traffic Operations Division, when an ESL is no longer necessary to attain
or maintain the NAAQS or fulfill transportation conformity requirements.
The amendments to §25.23 also provide the maximum allowable speed
reductions that will be considered for the state highway system as part of
a proposed ESL. The minimum allowable speed limit under this amendment as
part of an ESL is 45 miles per hour on a non-controlled access highway and
55 miles per hour on a controlled access highway. These restrictions will
ensure that any ESL enacted on the state highway system falls within a reasonable
minimum speed limit.
Section 25.24 (b) is amended by adding new paragraph (8)(A) describing
the process the department will use to evaluate an ESL. The amendment requires
that an ESL may only be submitted by the TNRCC to the Texas Transportation
Commission through the department's Traffic Operations Division. This amended
section further states that if such a proposal is not in accordance with the
criteria outlined in §25.23(f), the department will reject the request.
The Traffic Operations Division will evaluate the proposal for initial compliance
with the criteria described in §25.23(f). The Texas Transportation Commission
will make the final decision on approval or rejection of the proposed ESL.
These provisions are included to ensure that any proposed ESL is developed
by the authorized state agency responsible for air quality and that such a
speed reduction is designed to improve regional air quality. New paragraph
(8)(B) states that upon approval of an ESL, the department will install all
signs related to the new speed limit. This paragraph also specifies that cities
will not be required to establish ESL by city ordinance or resolution. ESL
will be established solely by commission minute order under the commission's
existing statutory authority to establish and alter speed limits on any portion
of the designated state highway system.
COMMENTS
The department received two sets of written comments on the proposed revisions.
Comment: One of these comments was from Jeffrey A. Saitas, Executive Director
of TNRCC. In his comment Mr. Saitas noted that his agency agreed with the
department's approach. In particular, Mr. Saitas noted that it was appropriate
for the TNRCC to be responsible for studying proposed environmental speed
limits and for making recommendations for such reductions to TxDOT based on
environmental/air quality studies. Mr. Saitas also stated his intention to
coordinate any proposed environmental speed limits with metropolitan planning
organizations to ensure that the appropriate roadways will be selected to
provide the greatest benefit to the area in question.
Comments were also received in regard to the proposed revision from Michael
Morris, Director of Transportation for the North Central Texas Council of
Governments (NCTCOG).
Mr. Morris' first comment concerned the impact an environmental speed limit
reduction may have on a nonattainment area's overall emissions budget. Mr.
Morris indicated that the NCTCOG would like assurances that the tradeoff between
on-road mobile sources and off-road mobile, stationary, and point sources
does not cause lower on-road motor vehicle emission budgets for conformity
requirements.
Response: The department recognizes and shares the concern that tradeoffs
in emission control strategies can have a negative impact on motor vehicle
emission budgets. The department does not have the final authority on selected
control strategies in any nonattainment area and cannot offer assurances that
motor vehicle emission budgets will not be changed during the SIP development
process. We have transmitted a copy of these comments to the TNRCC for its
consideration. The final selection of control strategies is under the authority
of the TNRCC. Our understanding is that control strategies are influenced
by the public hearing process.
Comment: Mr. Morris also stated that the NCTCOG has concerns that the department
may lower speed limits beyond local interest, thereby resulting in safety
concerns for the region.
Response: In response, the department would like to note that the safety
of the travelling public is always our highest priority. The department will
continually monitor any implemented environmental speed limits and make adjustments
as necessary to ensure motorist safety.
Comment: Mr. Morris' final comment involves the procedure by which a proposed
speed limit reduction would be made by TNRCC. The NCTCOG has requested that
the proposed rules be modified to require that the TNRCC allow metropolitan
planning organizations to comment on the request prior to submittal to the
Texas Transportation Commission.
Response: Environmental speed limits will only be proposed when they are
part of a nonattainment area's air quality plan or as part of such an area's
demonstration of transportation conformity. Metropolitan planning organizations
are an integral part of the transportation conformity process and will be
involved in any decisions to alter speed limits for transportation conformity
purposes MPOs are ultimately responsible for the transportation conformity
determination and will definitely have a major role in any decision making
on speed limit adjustments for transportation conformity purposes. The department
does not feel that the rules should be changed to formalize MPO comments.
In the SIP development process, decisions to alter speed limits will ultimately
be made by the TNRCC and not by the department. The department is the implementing
agency under these conditions and is not the regulatory agency. Comments about
the speed limit changes in the SIP process should be addressed to the TNRCC
through local task force groups or through the public hearing process. Again,
we have transmitted a copy of these comments to the TNRCC for its consideration.
The TNRCC has expressed its intention to coordinate all proposed environmental
speed limits with metropolitan planning organizations to ensure that the appropriate
roadways will be selected and to provide the greatest benefit to the area
in question.
No changes to the proposed rules have been made due to comments received.
However, to clarify the intent of amended §25.23(f) the department is
adopting this section with changes in subsection (f)(1) and (2). These changes
will allow the TNRCC to propose reductions in the existing posted speed limit
on portions of the state highway system for environmental consideration. These
reductions would either have to be part of TNRCC's State Implementation Plan
(SIP) designed to ensure that areas attain and maintain federal air quality
standards or be part of the areas transportation conformity determination.
The phrase "maintain the National Ambient Air Quality Standards" was intended
to refer to maintenance areas that must maintain the NAAQS through its 20-year
maintenance period. This phrase has been deleted in both paragraphs to avoid
the misconception that the ESL will be used in attainment counties that are
not covered by a SIP. ESLs may be used in nonattainment, maintenance, and
those attainment areas covered by state implementation plans.
Additionally, §25.23(f)(2) has been changed for clarification with
revisions to the following sentence: "In the event that the TNRCC determines
that an ESL is no longer necessary as a SIP requirement to attain and maintain
the NAAQS or to fulfill transportation conforming requirements, the TNRCC
shall notify the commission, through the Traffic Operations Division, that
the ESL is no longer necessary." The phrase "as a SIP requirement" has been
added to define a condition with TNRCC might request that an ESL might be
removed by TNRCC.
STATUTORY AUTHORITY
The amendments are adopted under Transportation Code, §201.101, which
provides the Texas Transportation Commission with the authority to establish
rules for the conduct of the work of the Texas Department of Transportation;
Transportation Code, §203.002, which authorizes the Texas Transportation
Commission to lay out, maintain, construct, and operate a modern state highway
system; and more specifically, Transportation Code §545.353, which authorizes
the Texas Transportation Commission to adopt procedures that will be used
to determine speed limits on the state highway system.
§25.23.Speed Zone Studies.
(a)
Overview.
(1)
Engineering and traffic investigation.
(A)
This section includes a description of how to conduct an
engineering and traffic investigation as the basis for establishing a regulatory
speed zone along a roadway. This investigation is commonly called a speed
zone study.
(B)
Sound and generally accepted engineering practices are
an integral part of speed zone studies and are discussed in subsection (d)
of this section.
(2)
Scope of study.
(A)
The speed zone study should cover the entire length of
a potential zone, even though an analysis of the data may later indicate that
the actual limits of the area that requires zoning are less than the limits
of the potential zone.
(B)
A speed zone study consists of the following principle
areas:
(i)
determining the 85th percentile speed;
(ii)
crash study;
(iii)
developing of strip maps;
(iv)
speed zone design; and
(v)
rechecks of speed zones.
(b)
Determining the 85th percentile speed.
(1)
General concepts.
(A)
The maximum speed limits posted as the result of a study
should be based primarily on the 85th percentile speed, when adequate speed
samples can be secured.
(B)
The 85th percentile speed is a value that is used by many
states and cities for establishing regulatory speed zones.
(2)
Theory. Use of the 85th percentile speed concept
is based on the theory that:
(A)
a speed at or below which 85 percent of people drive at
any given location under good weather and visibility conditions may be considered
as the maximum safe speed for that location; and
(B)
the large majority of drivers:
(i)
are reasonable and prudent;
(ii)
do not want to have a crash; and
(iii)
desire to reach their destination in the shortest possible
time.
(3)
Statistical rationale.
(A)
The results of numerous and extensive before-and-after
studies substantiates the general propriety and value of the 85th percentile
criterion.
(B)
Statistical techniques show that a normal probability distribution
will occur when a random sample of traffic is measured. From the resulting
frequency distribution curves, one finds that a certain percentage of drivers
drive too fast for the existing conditions and a certain percentage of drivers
travel at an unreasonably slow speed compared to the trend of traffic.
(C)
Most cumulative speed distribution curves break at approximately
15% and 85% of the total number of observations as shown in the following
Figure 1.
Figure 1: 43 TAC §25.23(b)(3)(C) (No change.)
(i)
Consequently, the motorists observed in the lower 15% are
considered to be traveling unreasonably slow; and those observed above the
85th percentile value are assumed to be exceeding a safe and reasonable speed.
(ii)
Because of the steep slope of the distribution curve below
the 85th percentile value, it can readily be seen that posting a speed below
the critical value would penalize a large percentage of reasonable drivers.
(D)
The example illustrated in Figure 1 as shown in subparagraph
(C) of this paragraph shows that a speed posted for 7 miles per hour below
the 85th percentile speed would unfairly penalize 25% of the drivers who would
otherwise be considered to be driving at a reasonable and prudent speed. Therefore,
for purposes of speed zoning:
(i)
the maximum posted speed should be as near as possible
to the 85th percentile value, and
(ii)
whenever minimum speed zones are used, the minimum posted
speed should be within 5 miles per hour of the 15th percentile value (See
25.22(b) of this title (relating to Regulatory Speed Zones) for additional
information on minimum speed limits).
(E)
Experience proves these findings valid and shows that the
85th percentile speed is the one characteristic of traffic speeds that most
closely conforms to a speed limit which is considered safe and reasonable.
(4)
Speed checks for existing highways are of prime
importance, because they:
(A)
represent the consensus of drivers as to the safe speed
at a given location; and
(B)
provide the basic data on which the regulatory speed zone
is based.
(5)
Speed checks for new or reconstructed highways.
(A)
Speed checks on new or reconstructed highway sections should
not be performed until it is apparent that the traffic speeds have stabilized.
(B)
As an interim measure, the statewide maximum speed or the
design speed of the roadway may be posted on these sections while utilizing
warning signs with advisory speed signs to alert drivers to any hazards. In
any case, trial run data should be collected and considered by a traffic engineer
before interim speed zones are posted. Once the traffic speeds have stabilized,
normal speed zone studies should be completed and evaluated by a traffic engineer
before the final speeds are posted.
(C)
Speed checks should be made as quickly as possible, but
it is not necessary to check the speed of every car. In many cases, traffic
will be much too heavy for the observer to check all cars.
(6)
Operation of speed check stations.
(A)
Normal speed checks should:
(i)
be made on average week days during off-peak hours under
normal traffic conditions;
(ii)
be made under favorable weather conditions;
(iii)
include only "free floating" vehicles (see subparagraph
(B) of this paragraph);
(iv)
include a minimum of 125 cars in each direction at each
station; and
(v)
be discontinued after two hours, even if 125 cars have
not been timed.
(B)
The vehicles checked should be only those in which drivers
are choosing their own speed ("free floating").
(i)
When a line of vehicles moving closely behind each other
passes the speed check station, only the speed of the first vehicle should
be checked, since the other drivers may not be choosing their own speed.
(ii)
Cars involved in passing or turning maneuvers should not
be checked, because they are probably driving at an abnormal rate of speed.
(C)
Trucks and buses should be recorded separately and should
not be included as part of the 125-car total.
(7)
Location of speed check stations.
(A)
A complete picture of speeds in an area can only be obtained
through the proper location of speed check stations. Ideally, speed checks
at an infinite number of locations would be desirable. However, since this
is not practical, speed check stations must be strategically located to show
all the important changes in prevailing speeds.
(B)
In urban areas and on approaches to cities, speed check
stations:
(i)
should generally be located at intervals of 0.40 kilometer
(0.25 mile) or less if necessary to insure an accurate picture of the speed
pattern;
(ii)
should be located midway between signals or 0.3 kilometer
(0.2 miles) from any signal, whichever is less, to ensure an accurate representation
of speed patterns;
(iii)
should take into account the locality and the uniformity
of physical and traffic conditions;
(iv)
may be determined by trial runs through the area if volumes
are too low or if a recheck of speeds is all that is needed; and
(v)
should be checked midway between interchanges on the main
lanes of expressways and freeways.
(C)
In rural areas, speed check stations:
(i)
may be at intervals greater than 0.40 kilometer (0.25 mile),
as long as the general speed pattern is followed;
(ii)
may only be necessary at each end and the middle point
in low volume sections; and
(iii)
may be determined by trial runs through the area.
(8)
Measuring speeds.
(A)
Radar speed meters which operate on the radar principle
are normally used for making speed checks. These devices operate from the
power of an automobile battery and give direct readings of vehicle speeds
in miles per hour which are accurate to within 2 miles per hour.
(B)
New technologies may be used in determining vehicular speeds
for use in calculating 85th percentile speed if the measured speeds are accurate
to within 2 miles per hour and the gap between vehicles is 3 seconds or greater.
Examples of new technologies are counter-classifiers with the capability of
classifying vehicles, determining vehicular speeds, and differentiating the
gap between vehicles. These devices may include video imaging, tube counters,
magnetic counters, inductive counters, etc.
(9)
Recording measured speeds.
(A)
Use TxDOT Form 1882, "Radar Motor Vehicle Speed Field Tally
Sheet," to record tally marks beside the observed speed for each vehicle.
Copies may be obtained from the Traffic Operations Division.
(B)
The following Figure 2 shows an example of a completed
Field Tally Sheet.
Figure 2: 43 TAC §25.23(b)(9)(B) (No change.)
(10)
Calculating 85th percentile speed.
(A)
Use the following procedure to calculate the 85th percentile
speed.
(i)
Add the tally marks as shown in the Cumulative Total column
in Figure 2 as shown in paragraph (9)(B) of this subsection. Note that the
marks are added from the bottom up.
(ii)
For each Cumulative Total column, calculate 85% of the
total number of vehicles checked. (EXAMPLE: Figure 2 shows that 125 cars were
counted in the northbound direction. So 85% would be 106 (125 x 0.85 = 106).
Thus, the 106th car (counting up from the bottom) represents the 85th percentile
speed.)
(iii)
Determine the speed at which the car representing the
85th percentile was traveling. Again from the northbound example in Figure
2, the 106th car was traveling at 48 miles per hour. Thus, 48 miles per hour
is the 85th percentile speed.
(B)
In Figure 2 as shown in paragraph (9)(B) of this subsection,
there is an "85th Percentile Calculation Table," which may be used to readily
determine the 85th percentile car if the total number is between 80 and 239.
(C)
In no case shall the 85th percentile speed be interpolated
between two speeds in the M.P.H. column.
(D)
After the locations of the speed check stations have been
decided upon and the speed checks have been made, the 85th percentile speeds
should be calculated immediately in the field. By doing so, it is possible
to get an idea of what the speed curve will look like and to determine if
more speed check stations are needed.
(11)
Recording the information.
(A)
Record the speed check data on the strip map as described
in subsection (c) of this section.
(B)
The blocks shown on the strip map contain the 85th percentile
speed, the speed of the fastest car checked, and the number of cars checked
(reading from top to bottom in order).
(C)
Show a block for each speed check location for each direction
of travel measured.
(12)
Incomplete data. When the data appear incomplete
because of a large change in the 85th percentile speed between speed check
stations or an unusually high or low 85th percentile speed at a particular
point, additional speed checks should be made at new locations or repeat checks
should be made at certain locations previously checked to clarify the speed
picture.
(c)
Developing strip maps
(1)
Strip map blanks.
(A)
The first step in establishing a speed zone is the preparation
of the strip map on which the data pertinent to the speed zone are recorded.
(B)
The map should be drawn on a strip map blank. These blanks
are available at the Traffic Operations Division as a graphics file or as
printed blanks. The following Figure 3 shows a sample strip map blank reduced
in size.
Figure 3: 43 TAC §25.23(c)(1)(B) (No change.)
(C)
The blank is intended to ensure uniformity and reduce drafting
work in the districts.
(2)
Scale for strip map.
(A)
The scale used on the Road Inventory (RI-1) Highway Log
Sheets is generally suitable for the strip map. In some cases, however, such
as in highly developed areas, a scale of 1 inch = 300 feet is preferred. In
sparsely developed rural areas, the RI-1 scale should be satisfactory. See
the following Figure 4 for an example RI-1 sheet.
Figure 4: 43 TAC §25.23(c)(2)(A) (No change.)
(B)
Two different scales should not be used on the same strip
map sheet. If, in zoning a long continuous section of highway, it is desirable
to change the scale on the strip map, then another strip map sheet should
be used for the beginning of the new scale.
(3)
Field entry data.
(A)
The strip map should be made complete by entering field
data to show road details in every aspect. The headings on the strip map blank
indicate much of the required data. The following Figure 5 through Figure
8 show examples of how the data should be presented.
Figure 5: 43 TAC §25.23(c)(3)(A) (No change.)
Figure 6: 43 TAC §25.23(c)(3)(A) (No change.)
Figure 7: 43 TAC §25.23(c)(3)(A) (No change.)
Figure 8: 43 TAC §25.23(c)(3)(A) (No change.)
(B)
If the roadway is not divided, it is not necessary to repeat
the right of way and roadbed width, surface width and type, grades over three
percent, and curves over two degrees for both directions of travel.
(C)
In addition to the preprinted information on the far left
of the strip map blank, the information in the following table should be shown:
Figure 9: 43 TAC §25.23(c)(3)(C) (No change.)
(4)
City limits.
(A)
At locations where the study is extended into or through
an incorporated city, the zone should be broken at the city limit, regardless
of whether the zone speed changes. This is necessary because the speed limits
inside the limits of an incorporated city may be established by the city government,
while the speed limits outside the corporate limits of a city must be established
by the commission.
(B)
It is also necessary to show on the strip map the precise
location of the city limit either by reference marker or milepoint and control
section to prevent misinterpretation of the zone when the city limit is changed.
The zone speed of any adjoining map should always be shown.
(C)
In the event the city limit is changed, the strip map and
commission minute order should be revised to show the new city limit.
(5)
Schools.
(A)
If a reduced school speed limit is warranted, a speed zone
strip map should be prepared as shown in the following Figures 10 and 11.
Figure 10: 43 TAC §25.23(c)(5)(A) (No change.)
Figure 11: 43 TAC §25.23(c)(5)(A) (No change.)
(B)
A regular speed zone must not change within the limits
of a school speed zone since posting of a regular speed zone sign at the point
of change would prematurely terminate the school speed zone. This is due to
the fact that speed limits remain fixed until a revised limit is encountered.
(C)
Speed checks provide a sound basis for selecting the proper
speed limits for school zones. While it is not common practice to set speed
limits significantly lower than the 85th percentile speed for regulatory speed
zones, exceptions to this practice are often found at school zones.
(D)
Factual studies, reason, and sound engineering judgement,
rather than emotion, should govern the final decision on the maximum deviation
from the 85th percentile speed which will provide a reasonable and prudent
speed limit.
(E)
It is not advisable to set a school speed limit above 35
miles per hour in either rural or urban areas. Lower school speed limits should
be considered when the 85th percentile speed is below 50 miles per hour.
(F)
When the results of a speed study indicate an 85th percentile
speed below 50 miles per hour, the reduced school speed limit should not be
more than 15 miles per hour below the 85th percentile speed or normal posted
speed limits. If the 85th percentile speed is 55 miles per hour, the reduced
school speed limit should be 20 miles per hour below the 85th percentile speed.
Any roadway with an 85th percentile speed greater than 55 miles per hour requires
a buffer zone to transition down to a 35 mile per hour speed limit.
(6)
Showing crashes on strip maps.
(A)
At locations where recommended speed zones will be 5 miles
per hour or more below the 85th percentile speed because of high crash experience,
the crashes for the most recent calendar year available should be shown on
the strip map. RI-1 Sheets will facilitate accurate plotting of crashes, since
crash locations are coded from these sheets.
(B)
When districts submit strip maps or prints to the Traffic
Operations Division for review, TRF will obtain the crash rate for the roadway
section in question as well as the statewide average crash rate for the appropriate
type of roadway section and add these data to the strip map. Crash rates will
be considered before lowering the zone. These data will be an important consideration
in determining whether the lower zoning is justified.
(C)
Crash data need not be plotted on the strip map when proposed
speed zones are within 5 miles per hour of the 85th percentile speed checks.
(d)
Speed zone design.
(1)
Zone length.
(A)
The length of any section of zone set for a particular
speed should be as long as possible and still be consistent with the 85th
percentile speeds. These zone lengths should be shown on the strip map in
miles to three decimal places. Where graduated zones on the approach to the
city are at locations where speeds fluctuate, the speed zone should generally
be 0.322 kilometer (0.200 mile) or more.
(B)
School zones are the exception to this rule and may be
as short as reasonable in urban areas, depending on approach speeds.
(i)
School zones in urban areas where speeds are 30 miles per
hour or less may have school zones as short as 60.96 to 91.44 meters (200
to 300 feet).
(ii)
Where speeds exceed 40 miles per hour, the minimum school
zone length should be 304.80 meters (1,000 feet) to allow for normal deceleration.
(2)
Transitions.
(A)
The change in speed between two adjacent zones should not
normally be greater than 15 miles per hour, because the change in speed would
be too abrupt for driver observance.
(B)
If adjacent 85th percentile speeds show an abrupt change
of more than 15 miles per hour, a transition zone of approximately 0.32 kilometer
(0.200 mile) or more in length should be used.
(3)
Urban areas. Texas law states that the maximum
speed limit through an urban district is 30 miles per hour, unless zoned otherwise
by proper authority. A reasonable and prudent speed limit should be determined
and negotiated with the city and set by city ordinance or resolution or by
commission minute order. A section of highway in this category should be speed
zoned by commission minute order only if all negotiations with the city have
proved unsuccessful.
(4)
Directional differences.
(A)
The 85th percentile speeds may differ considerably by direction
at some locations. Such conditions are usually caused by relatively heavy
development on one side of the road. Next to the development, motorists will
tend to drive slower because of interference from traffic to and from the
development.
(B)
On divided highways, the zone speeds should conform to
the 85th percentile speed even though this may require zoning for different
speeds in opposite directions.
(C)
On undivided roadways, the zones in opposite directions
should be the same for enforcement purposes.
(5)
Variation from 85th percentile.
(A)
The posted speed selected is the nearest value ending in
5 or 0. The final speed limit may be lowered or raised by as much as 5 miles
per hour from the 85th percentile speed determined by the study, based on
the professional judgement of the supervising engineer. Only under special
conditions would the zone speed vary further from the 85th percentile. Explanations
of such conditions follow.
(i)
Different results at adjacent speed check stations. If
the 85th percentile speeds for adjacent speed check stations are approximately
the same, they may be averaged to determine the zone speed. Any 85th percentile
speed should not be included in such averages if it varies more than 7 miles
per hour from the speed derived from the average.
(ii)
Crash rate greater than average. On a section of highway
having a crash rate greater than the statewide average crash rate for the
same type of roadway section, the zone speed may be as much as 7 miles per
hour lower than the 85th percentile speed. NOTE: This should be considered
more as an exception than as a rule, and should be done only when enforcement
agencies will assure a degree of enforcement that will make the speed zone
effective.
(iii)
Light traffic volumes. At locations where traffic volumes
are light and 125 cars cannot be checked in the two hours that the speed check
station is operated, the 85th percentile speed may not be reliable. Trial
runs need to be made and documented in the study. ("Trial runs" are defined
and explained in paragraph (7) of this subsection.) Trial runs may be documented
using the "Summary of Trial Run for Speed Zones" (TxDOT Form 1929) instead
of a strip map. Copies may be obtained from the Traffic Operations Division.
The following Figure 12 shows an example of a completed Summary of Trial Run
for Speed Zones.
Figure 12: 43 TAC §25.23 (d)(5)(A)(iii) (No change.)
(iv)
Legislative or congressional action. Notwithstanding the
volume of traffic, if legislative or congressional action results in the immediate
increase in statewide maximum legal speed limits, then reasonable and prudent
speed zones may be established by trial runs and engineering judgment in lieu
of other speed check procedures provided in this subchapter. Trial runs may
be documented using the Summary of Trial Run for Speed Zones (TxDOT Form 1929)
instead of a strip map. Speed zones established through this process should
be rechecked in accordance with the procedure in subsection (e) of this section.
(v)
Additional roadway factors. The posted speed limit may
be reduced by as much as 10 miles per hour (12 miles per hour for locations
with crash rates higher than the statewide average) below the 85th percentile
speed, based on sound and generally accepted engineering judgement that includes
consideration of the following factors:
(I)
narrow roadway pavement widths: 20 feet (6.1 m) or less,
for example;
(II)
horizontal and vertical curves (possible limited sight
distance);
(III)
hidden driveways and other developments (possible limited
sight distance);
(IV)
high driveway density (the higher the number of driveways,
the higher the potential for encountering entering and turning vehicles);
(V)
crash history along the location;
(VI)
rural residential or developed areas (higher potential
for pedestrian and bicycle traffic); and
(VII)
lack of striped, improved shoulders (constricted lateral
movement).
(B)
Local public opinion may also be considered on farm-to-market
and ranch-to-market roads without improved shoulders (Transportation Code,
Section 545.3535(b)).
(C)
The final decision on the amount of variation from the
85th percentile speed for a specific roadway should be based on the engineering
judgment of the supervising engineer.
(D)
Speed limits should not be posted more than 10 miles per
hour (12 miles per hour for locations with crash rates higher than the statewide
average) below the 85th percentile, since unreasonably low speed limits have
not been shown to be an effective way to control speeding. Allowing too great
a variation would risk losing motorist respect for speed limits and traffic
control devices.
(6)
Blanket lowering of maximum speed limits. Blanket
lowering of speed limits may be justified to avoid non-compliance with direct
requests from the federal government to lower the statewide maximum speed
limit.
(7)
Trial runs.
(A)
A "trial run" is a drive through the speed zoned section
of roadway at the chosen speed(s) to determine if the speeds are appropriate
for the area. An average passenger vehicle along with a reasonably competent
driver should be selected. An "average passenger vehicle" should be somewhat
representative of most vehicles on the highway.
(B)
After the 85th percentile speeds and zone lengths have
been selected, several trial runs should be made through the area in both
directions driving at the selected speeds. This should show any irregularities
in the zoning which need correction.
(C)
Documentation. Trial runs may be documented using the Summary
of Trial Run for Speed Zones (TxDOT Form 1929) instead of a strip map.
(8)
Location of regulatory speed limit signs.
(A)
Speed zones are legally described to the nearest thousandth
of a mile (5 feet). Regulatory speed limit signs should be located within
approximately 1.6 meters (5 feet) of the actual reference marker or milepoint
defined in the minute order or city ordinance or resolution.
(B)
The locations of regulatory speed zones tied to speed changes
should be examined carefully to ensure that signs can be erected within the
1.6 meters (5 feet) variation. If adherence to the 1.6 meters (5 feet) variation
is not possible, the speed zone sign should be placed as close to the actual
location defined in the minute order or city ordinance or resolution as practical.
(e)
Rechecks of speed zones.
(1)
Introduction.
(A)
The basic data on which speed zones are established are
subject to change when conditions change, and established speed zones must
not be considered permanent.
(B)
Physical improvements to the roadway, increased roadside
development, and heavy increases in traffic volumes justify a recheck of speeds
to determine whether the 85th percentile speed has changed enough to require
a change in the zone speeds.
(2)
Frequency of rechecks.
(A)
Periodic rechecks of all zones are desirable at intervals
of about three to five years in urban areas regardless of roadway improvements,
roadside developments, or increases in traffic volumes. Trial runs or rechecks
of every third speed check station may be made.
(B)
Rechecks in rural areas are desirable at intervals of five
to ten years. In many instances, trial runs may be sufficient.
(C)
If the speed checks or trial runs indicate a need for revision
of the zone, rechecks of speeds should be made at all speed check stations
for that particular section and a revised strip map made and submitted.
(3)
Procedure.
(A)
In preparing a revised strip map, the original tracing
on file with the Traffic Operations Division may be obtained and used where
all data, other than speed check data shown on the map, are current. A strip
map containing out of date information should be considered obsolete.
(B)
New strip maps should be prepared when physical improvements
of the roadway have been made or when changes in roadside development have
occurred since the original strip map was prepared even though the speed checks
and zone speeds may not change.
(f)
Environmental speed limits.
(1)
Environmental speed zone study. TNRCC is responsible for
making the study of proposed environmental speed limits and their locations
based on TNRCC environmental/air quality studies and modeling considerations.
Since reduced speeds can have a positive effect on air quality, environmental
speed limits (ESLs) may be implemented on roadways for which an environmental/air
quality study demonstrates that the ESL will measurably contribute to meeting
SIP requirements, or fulfilling transportation conformity requirements.
(2)
Scope and details of an environmental speed zone study.
The environmental speed zone study shall describe all the proposed highways
and the proposed locations of each environmental speed limit (ESL). A written
description shall define where each different ESL begins and ends as well
as the individual proposed speed. An ESL is a reduced regulatory speed limit
identified as a control measure in a SIP or to fulfill transportation conformity
requirements. An ESL may be implemented on roadways if an environmental/air
quality study indicates that reduced speed limits can measurably contribute
to attaining the NAAQS or to fulfilling transportation conformity requirements.
On controlled access roadways, an ESL may be set 5, 10, or 15 m.p.h. below
existing regulatory speeds, except that no ESL may be less than 55 m.p.h.
On non-controlled access roadways, an ESL may be set at 5, 10, or 15 m.p.h.
below existing regulatory speeds, except that no ESL may be less than 45 m.p.h.
In the event that the TNRCC determines that an ESL is no longer necessary
as a SIP requirement to attain and maintain the NAAQS or fulfill transportation
conformity requirements, the TNRCC will notify the commission, through the
Traffic Operations Division, that the ESL is no longer necessary. The term
"existing regulatory speeds" as mentioned in this paragraph only applies to
speed limits established under a speed zone study that used the 85th percentile
speeds to establish the speed zone.
This agency hereby certifies that the adoption has been
reviewed by legal counsel and found to be a valid exercise of the agency's
legal authority.
Filed with the Office of
the Secretary of State on May 26, 2000.
TRD-200003766
Richard Monroe
General Counsel
Texas Department of Transportation
Effective date: June 15, 2000
Proposal publication date: March 10, 2000
For further information, please call: (512) 463-8630