Signal Clearance Intervals
Signal clearance intervals are intended to allow those roadway users who are approaching a traffic signal that changes to yellow, and cannot stop before the signal turns red, time to enter and clear the intersection before the cross-street traffic is given a green light. Signal clearance intervals include both the yellow interval and any all-red interval. For motor vehicles, clearance intervals are typically a maximum of five seconds. Table 21 shows the number of seconds required for the 85th percentile user for various vehicular types to clear roadways of a given width. Additionally, the AASHTO calculated values (assuming acceleration rates of 1.2 m/sec2 (4 ft/sec2)) are shown. Manual wheelchair users had the longest 85th percentile clearance intervals (greater than those provided by the AASHTO assumptions), indicating that they would need the most time to clear the intersection.
Table 21. 85th percentile clearance intervals (sec).
| USER TYPE | WIDTH OF DEVICE PLUS WIDTH OF ROADWAY | |||
|---|---|---|---|---|
| 6.1 m | 12.2 m | 18.3 m | 24.4 m | |
| Bicycle | 4.85 | 5.53 | 6.21 | 6.89 |
| Hand cycle | 5.09 | 5.88 | 6.67 | 7.46 |
| Inline skates | 7.97 | 8.62 | 9.27 | 9.92 |
| Kick scooter | 7.53 | 8.55 | 9.56 | 10.58 |
| Manual wheelchair | 8.29 | 10.12 | 11.95 | 13.77 |
| Power wheelchair | 4.55 | 5.87 | 7.19 | 8.51 |
| Recumbent bicycle | 3.41 | 3.92 | 4.42 | 4.93 |
| Segway | 5.50 | 6.40 | 7.31 | 8.21 |
| AASHTO signal | 5.50 | 5.50 | 6.50 | 7.50 |
| Pedestrian clearance | 5.00 | 10.00 | 15.00 | 20.00 |
The kick scooter is the critical user with respect to clearance intervals for traffic signals if it is legal for kick scooters to operate on the street.
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