1. A 40 mph minimum design speed may be used where roadside environment or unusual design considerations dictate (e.g., significant horizontal curvature due to mountainous or hilly terrain).

2. A 30 mph minimum design speed may be used where roadside environment or unusual design considerations dictate (e.g., significant horizontal curvature due to mountainous or hilly terrain).

3. Applicable only to off-system routes that are not functionally classified at a higher classification.

4. Referenced from AASHTO A Policy on Geometric Design of Highways and Streets, 2018, 7th Edition.

1. In highly restricted locations or locations with less than 5% trucks and speeds less than or equal to 40 mph, 10- ft lane is permissible. Engineering judgement should be exercised when determining if 10-ft is acceptable and must be approved by the District. Use of 10-ft travel lanes must be approved by the District and approval documented in the project file. If the District approves the use of 10-ft lanes, a design exception would not be required.

2. "DS" stands for Design Speed

3. 9-ft minimum lane width in residential areas. 10-ft minimum lane width in non-industrial areas. 11-ft minimum lane width in industrial areas.

4. Applicable only to off-system routes that are not functionally classified at a higher classification.

5. 24-ft minimum surfacing width for all on-system state highway routes.

6. On high riprapped fills through reservoirs, a minimum of two 12-ft lanes with 8-ft shoulders should be provided for roadway sections. For arterials with ≥ 2000 ADT in reservoir areas, two 12-ft lanes with 10-ft shoulders should be used.

7. Minimum width of new or widened structures should accommodate the approach roadway including shoulders.

8. A minimum surfacing width of 36-ft should be considered on horizontal curves with a radius less than 190-ft (i.e., greater than 3 degrees of curvature). See FHWA Handbook for Designing Roadways for the Aging Population for further recommendations on minimum pavement width in horizontal curves when considering older drivers.

9. 12-ft lanes are permissible on ramps and direct connectors with multiple lanes.

1. Full minimum width of shoulder should be fully surfaced. Where wider shoulder widths are used, partial (not less than minimum width) surfacing or full width surfacing may be provided at the option of the designer.

2. On high riprapped fills through reservoirs, a minimum of two 12-ft lanes with 8-ft shoulders should be provided for roadway sections. For arterials with ≥ 2000 ADT in reservoir areas, two 12-ft lanes with 10-ft shoulders should be used.

3. Minimum width of new or widened structures should accommodate the approach roadway including shoulders.

4. A minimum surfacing width of 36-ft should be considered on horizontal curves with a radius less than 1910-ft (i.e., greater than 3 degrees of curvature). See FHWA Handbook for Designing Roadways for the Aging Population for further recommendations on minimum pavement width in horizontal curves when considering older drivers.

5. On arterials, shoulders should be fully surfaced.

6. 4-ft minimum shoulder if longitudinal barrier is used. The shoulder across a bridge will be measured from the travel lane edge to the nominal face of rail. This provides additional offset for high-speed operation and door-opening space for vehicles stopped on the shoulder of the roadway.

7. On collectors, shoulders must be fully surfaced on collectors with ≥ 1500 ADT. Shoulder surfacing not required but is desirable even if only for minimum width on collectors with < 1500 ADT on all local roads.

8. Applicable only to off-system routes that are not functionally classified at a higher classification.

9. 5-ft minimum clear space (shoulder) for bicyclists should be provided on bridges being replaced or rehabilitated, except on off-system facilities with less than 400 ADT. For off-system bridges with current ADT greater than 400 ADT, the 5-ft additional shoulder width may be excepted through the Design Exception process from the bicycle clear space requirement if the additional width represents an unreasonable increase in cost.

10. Where left or right turn lanes are present on uncurbed facilities, a 4-ft fully surfaced shoulder must be provided.

11. In highly constrained conditions 8-ft may be used with engineering judgement, 10-ft is ideal

12. Mailbox Turnouts should be considered on local roads with ≥ 400 ADT. Refer to TxDOT standard drawings for details.

13. If sight distance restrictions are present due to horizontal curvature, swapping the widths of the inside and outside shoulders is allowed (i.e., the shoulder width on the inside of the curve may be increased to 6-ft minimum and the shoulder width on the outside of the curve decreased to 2-ft(Rdwy) or 4-ft(Str)) but can be no less than the values stated in this footnote (see Note 6).

14. On 4-lane undivided collector highways, outside surfaced shoulder width may be decreased to 4-ft where flat (1V:10H), sodded front slopes are provided for a minimum distance of 4-ft from the shoulder edge.

15. Arterials on the Texas Highway Freight Network (THFN) should provide 10-ft minimum outside shoulders.

16. For Direct Connectors 8’ minimum outside shoulder is required. No minimum shoulder with required on curbed ramps

17. On 6 lane or more divided arterials, 10-ft inside shoulders should be provided. The inside shoulder width may be reduced to 4-ft in constrained situations.

18. Referenced from AASHTO A Policy on Geometric Design of Highways and Streets, 2018, 7th Edition.

1. AASHTO uses Method 2 superelevation distribution. Method 2 only introduces superelevation after the maximum side friction has been used. Therefore, no superelevation is needed on flatter curves. This method is used on low-speed rural town, suburban, urban and urban core facilities where, because of various constraints, superelevation frequently cannot be provided.

2.Method 5 is intended to accommodate overdriving that is likely to occur on flat to intermediate curves. Overdriving on such curves involves little risk that a driver will lose control of the vehicle because superelevation sustains nearly all the lateral acceleration at the average running speed and a large amount of side friction is available for greater speeds.

3. Referenced from AASHTO A Policy on Geometric Design of Highways and Streets, 2018, 7th Edition.

1. SSD applies to horizontal alignments, and crest vertical curves for the purposes of a design exception. SSD for crest vertical curves is a direct correlation with the K-Value. If the minimum K-Value is satisfied for a crest vertical curve (Fig. 4-6), the vertical SSD is satisfied under the usual conditions.

2. Referenced from AASHTO A Policy on Geometric Design of Highways and Streets, 2018, 7th Edition.

1. Less than 15% maximum can be used in very constrained conditions. Flatter gradients should be used where practical and grades less than 5% are desirable

Notes:

1. Vertical clearance requirements include an additional 0.5-ft to accommodate future resurfacing as required by AASHTO’s A Policy on Geometric Design of Highways and Streets.

2. Intersecting roadway goes over the functionally classified roadway.

3. Exceptional cases near as practical to 16.5-ft but never less than 14.5-ft

4. Includes overhead signs, light fixtures, sign bridges, and toll gantries.

5. If an overlay reduces the vertical clearance below 18-ft, a TFHN Design Deviation will be required.

Notes:

1. Applicable to high volume (ADT ≥ 1500) roadways.

Notes:

1. Applicable to low volume and high volume roadways.

Notes:

1. Applicable to low volume and high volume roadways.

2. Shoulders width applicable to uncurbed sections, 0-ft minimum for curbed sections.

Notes:

1. Applicable to high volume (ADT ≥ 1500) roadways.

Notes:

1. Applicable to high volume (ADT ≥ 1500) roadways.

1. Applicable to high volume (ADT ≥ 1500) roadways

Notes:

1. Applicable to low volume and high volume roadways.

Notes:

1. Applicable to high volume (ADT ≥ 1500) roadways

Notes:

1. Applicable to high volume (ADT ≥ 1500) roadways

Notes:

Notes:

1. Stopping Sight Distance (SSD) applies to horizontal alignments and crest vertical curves for the purposes of a Design Exception. SSD for crest vertical curves is a direct correlation with the K-value. If the K-Value meets or improves the conditions of the remainder of the roadway, then the vertical SSD is satisfied under usual conditions

2. For approach roadways ≤ 24-ft.

3. For approach roadways > 24-ft, or the county or municipal entity has near term plans to widen the approach roadway or anticipates near term development.