Braking Distance on Grade
Braking distance on downgrade or upgrade, abbreviated as \(B_d\), is when the highway is on a grade. The steeper the downgrade the longer it takes to stop. The steeper the upgrade the shorter it takes to stop.
Braking Distance on downgrade or upgrade formulas |
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\(\large{ B_d = \frac{ V^2 }{ 30 \; \left( \frac{ a }{ 32.2 } \;\pm\; G \right) } }\) \(\large{ B_d = \frac{ V^2 }{ 30 \; \left[ \left(\frac{ a }{ 32.2 }\right) \;\pm\; \frac{ G }{ 100 } \right] } }\) |
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Symbol | English | Metric |
\(\large{ B_d }\) = braking distance on grade | \(\large{ft}\) | \(\large{m}\) |
\(\large{ a }\) = deceleration rate | \(\large{\frac{ft}{sec}}\) | \(\large{\frac{m}{sec}}\) |
\(\large{ V }\) = design speed | \(\large{\frac{ft}{sec}}\) | \(\large{\frac{m}{sec}}\) |
\(\large{ G }\) = grade percent divided by 100 | \(\large{dimensionless}\) |
AASHTO Exhibit 3-2 Stopping Sight Distance on grade |
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Design Speed | Stopping Sight Distance | |||||
Downgrade | Upgrade | |||||
3% | 6% | 9% | 3% | 6% | 9% | |
15 | 80 | 82 | 85 | 75 | 74 | 73 |
20 | 116 | 120 | 126 | 109 | 107 | 104 |
25 | 158 | 165 | 173 | 147 | 143 | 140 |
30 | 205 | 215 | 227 | 200 | 184 | 179 |
35 | 257 | 271 | 287 | 237 | 229 | 222 |
40 | 315 | 333 | 354 | 289 | 278 | 269 |
45 | 378 | 400 | 427 | 344 | 331 | 320 |
50 | 446 | 474 | 507 | 405 | 388 | 375 |
55 | 520 | 553 | 593 | 469 | 450 | 433 |
60 | 598 | 638 | 686 | 538 | 515 | 495 |
65 | 682 | 728 | 785 | 612 | 584 | 561 |
70 | 771 | 825 | 891 | 690 | 658 | 631 |
75 | 866 | 927 | 1003 | 772 | 736 | 704 |
80 | 965 | 1035 | 1121 | 859 | 817 | 782 |
Tags: Transportation Equations