Reference tables
Stopping sight distance tables
Transcribed verbatim from the source manuals. Values are published as printed, including where a table disagrees with the equation in the same document — those cells are marked and explained rather than corrected.
Need a value between these, or on a grade the tables don't list?Use the calculator.
Level grade — all published columns
Source: TxDOT, Roadway Design Manual, §4.11.1 Table 4-23. Comparison columns from Caltrans HDM Table 201.1 and FHWA-SA-10-001 Table 2. All values in feet.
| Speed | Reaction | Braking | Calculated | TxDOT design | Caltrans | Mean driver | Dry roadway |
|---|---|---|---|---|---|---|---|
| 15 mph | 55.1 | 21.6 | 76.7 | 80 | 100 | 40 | 75 |
| 20 mph | 73.5 | 38.4 | 111.9 | 115 | 125 | 60 | 110 |
| 25 mph | 91.9 | 60.0 | 151.9 | 155 | 150 | 80 | 150 |
| 30 mph | 110.3 | 86.4 | 196.7 | 200 | 200 | 105 | 190 |
| 35 mph | 128.6 | 117.6 | 246.2 | 250 | 250 | 135 | 235 |
| 40 mph | 147.0 | 153.6 | 300.6 | 305 | 300 | 165 | 285 |
| 45 mph | 165.4 | 194.4 | 359.8 | 360 | 360 | 200 | 340 |
| 50 mph | 183.8 | 240.0 | 423.8 | 425 | 430 | 235 | 400 |
| 55 mph | 202.1 | 290.3 | 492.4 | 495 | 500 | 275 | 465 |
| 60 mph | 220.5 | 345.5 | 566.0 | 570 | 580 | 320 | 535 |
| 65 mph | 238.9 | 405.5 | 644.4 | 645 | 660 | 365 | 605 |
| 70 mph | 257.3 | 470.3 | 727.6 | 730 | 750 | 415 | 680 |
| 75 mph | 275.6 | 539.9 | 815.5 | 820 | 840 | 465 | 765 |
| 80 mph | 294.0 | 614.3 | 908.3 | 910 | 930 | 520 | 850 |
- Calculated is the raw equation output. TxDOT design is that value rounded up to the next 5 ft, and is the value used in design.
- Caltrans is California's independently adopted minimum. It is not a rounding of the calculated column, which is why it diverges above 45 mph.
- Mean driver is what an average driver actually needs (1.1 s reaction, 17.71 ft/s²). It is a comparison published by FHWA, not a design standard.
- Dry roadway is published by FHWA without a stated deceleration rate, so this site reproduces it as reference data only and does not compute it.
On grade
Source: TxDOT Table 4-24. All values in feet. Downgrades require more distance because gravity works against braking.
| Speed | 3% down | 6% down | 9% down | 3% up | 6% up | 9% up |
|---|---|---|---|---|---|---|
| 15 mph | 80 | 82 | 86* | 75 | 74 | 73 |
| 20 mph | 116 | 120 | 126 | 109 | 107 | 104 |
| 25 mph | 158 | 165 | 173 | 147 | 143 | 140 |
| 30 mph | 205 | 215 | 227 | 200* | 184 | 179 |
| 35 mph | 257 | 271 | 287 | 237 | 229 | 222 |
| 40 mph | 315 | 333 | 354 | 289 | 278 | 269 |
| 45 mph | 378 | 400 | 427 | 344 | 331 | 320 |
| 50 mph | 446 | 474 | 507 | 405 | 388 | 375 |
| 55 mph | 520 | 553 | 593 | 469 | 450 | 433 |
| 60 mph | 598 | 638 | 686 | 538 | 515 | 495 |
| 65 mph | 682 | 728 | 785 | 612 | 584 | 561 |
| 70 mph | 771 | 825 | 891 | 690 | 658 | 631 |
| 75 mph | 866 | 927 | 1003 | 772 | 736 | 704 |
| 80 mph | 965 | 1035 | 1121 | 859 | 817 | 782 |
These published cells disagree with the equation printed in the same section. See the analysis below.
A discrepancy in Table 4-24 at 30 mph on a 3% upgrade
TxDOT Table 4-24 publishes 200 ft for a 30 mph design speed on a 3% upgrade. The grade equation printed in the same section of the same manual gives190 ft. This is set out here so it can be checked rather than taken on trust.
The arithmetic
§4.11.1 gives the braking distance on grade asdᵇ = V² / [30 × (a / 32.2 ± G)], with the brake reaction distance dᵣ = 1.47 × V × t. Using the manual's own stated values of t = 2.5 s and a = 11.2 ft/s², at V = 30 mph and G = +0.03:
| Brake reaction distance | 1.47 × 30 × 2.5 = 110.25 ft |
|---|---|
| Effective deceleration term | 11.2 / 32.2 + 0.03 = 0.377826 |
| Braking distance | 30² / (30 × 0.377826) = 79.40 ft |
| Total | 189.65 ft → 190 ft |
Three reasons 190 ft appears to be the intended value
- The equation in the same section gives it. No alternative set of stated assumptions in §4.11.1 produces 200 ft at this speed and grade.
- 200 ft breaks the ordering of its own row. The 6% and 9% upgrade values are 184 ft and 179 ft. An upgrade shortens the required distance because gravity assists braking, so the 3% value must fall between the level value and the 6% value. The level design value is also 200 ft, which is what the cell appears to have been filled with.
- Other AASHTO-derived state tables publish 190 ft. WSDOT Design Manual Chapter 1260 gives 190 ft for 30 mph on a 3% upgrade.
The value appears identically in the November 2024 PDF edition and in the current TxDOT web edition of §4.11.1, so it is not a transcription artefact at our end.
What this calculator does about it
It reports the equation result and shows the published value alongside it, rather than silently reproducing the table or silently correcting it. Thecalculator at 30 mph on a 3% upgrade displays both figures and this explanation. A regression test pins the discrepancy, so if a future TxDOT revision changes the cell, the test fails and this page gets updated rather than quietly drifting out of date.
This is a documentation discrepancy of about 10 ft at one cell of one table, not a safety finding. Design criteria are set by the agency with jurisdiction, and where a project is governed by TxDOT criteria the published table is what controls — verify against the current manual and confirm with the governing agency. It is recorded here because an engineer checking this calculator against the manual would otherwise find a difference and have no way to tell which was wrong.
Grades not shown in the table
The published grade table covers 3%, 6% and 9% only. Real alignments are rarely so convenient. The calculator applies the same equation continuously, so you can enter 4.5% or 7.2% and see the working rather than interpolating by hand.