Gap Acceptance
At streets that have no stop sign or traffic signal, pedestrians and drivers try to cross when there is a gap in traffic that is long enough to give them time to cross.
Traffic engineers have studied the gap acceptance of drivers for many years and found that the length of time for gaps that drivers consider acceptable:
- varies between geographical areas (for example drivers in the Mayagüez area of Puerto Rico accepted gaps that are shorter than those accepted by drivers in other regions)
- varies within individual drivers (drivers sometimes accepted a gap that was shorter than gaps they had already rejected)
The length of time for gaps that drivers found acceptable for entering the street to cross or turn can be also affected by such factors as:
- how many vehicles are waiting at the stop sign;
- how long the driver has waited at the stop sign once he got there;
- the volume of traffic on the major street;
- gender of the driver (in one study, age of driver seemed to have no effect but men accepted shorter gaps than women);
- whether the traffic on the main street travels in platoons from a signal upstream or with random gaps;
- whether the driver is going straight or turning left (drivers going straight accept shorter gaps than drivers turning).
Sources:
- Kittelson, W.K and Vandehey, M.A.(1991) Delay Effects on Driver Gap Acceptance Characteristics at two-way stop-controlled Intersections Transportation Research Record No. 1320. Transportation Research Board
- Solberg, P; Oppenlander, J C, (1966). Lag and Gap Acceptances at Stop-Controlled Intersections. Highway Research Record No. 122 Transportation Research Board ; Highway Research Board
- Jorge Jorge Rivera Rodríguez (2006) Gap Acceptance Studies and Critical Gap Times for Two-Way Stop Controlled Intersections in the Mayagüez Area
A project submitted in partial fulfillment of the requirements for the degree of
MASTERS OF ENGINEERING In CIVIL ENGINEERING, UNIVERSITY OF PUERTO RICO, MAYAGÜEZ CAMPUS
Final Report ThW94-04
- Dr. B. Kent Lall, Professor Dr. Jian John Lu (1994). Traffic Characteristics at Two-Way Stop-Controlled Intersections
- Gattis, J.L., Low, S.T. Gap Acceptance at Nonstandard Stop=Controlled Intersections.
MBTC FR 1059
quote from page 10:
For practical purposes, Highway Capacity Manual assumes that all drivers have consistent gap acceptance behavior; that is to say the accepted gaps are always greater than or equal to the critical gap [ed: "critical gap" is the gap length which half the drivers accept] (1).
According to Cassidy et al., this assumption is not always true because the gap acceptance process is probabilistic (13). Each driver has his or her own perception of a critical gap and the value of this "minimum acceptable" gap may change with conditions at the intersection. For instance, a driver may not always act consistently and may accept a subsequent gap that is smaller than previously rejected gaps.
1. Special Report 209: Highway Capacity Manual, 3rd ed. TRB, National Research Council,
Washington, D. C. 1994. pp. 10-3--10-12.
13. Cassidy, J. M., Madanat, S. M., Wang, M., and Yang, F. Unsignalized Intersection Capacity and Level of Service: Revisiting Critical Gap. Transportation Research Record 1484, TRB, National Research Council, Washington, D. C. 1995. pp. 16-23.
Return to Self-Study Guide: Crossable Gaps and Acceptable Gaps in Traffic