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Driveway Location and Spacing 23 and speed, the number of vehicles turning into the driveway, the type of traffic control at the driveway, and whether the subject driveway is on the same or opposite side of the road from the entry ramp. Where the ramp entry is signalized, signal spacing criteria should govern where access con- nections are provided. A time-space analysis of the signals along the arterial, including any ramp signalization, can help in identifying the best locations for signalized access. Unsignalized ramp entry junctions can be either stop- or yield-controlled, with a geometry that is either free flowing or one that forces the ramp vehicle to come to a stop before entering the road- way. If a driveway is too close to an upstream ramp that is entering an arterial, this can cause con- gestion with spillback onto the ramp and additional conflict on the through roadway segment. This concern can be heightened where there is insufficient distance for the following sequence to occur: vehicles exit the ramp, merge into the outside lane of a multilane arterial, weave across through travel lanes, and finally enter an inside or left-turn lane to turn into a driveway on the opposite side of the roadway from the ramp. Vehicles making this maneuver have to wait for gaps in the through traffic lanes before weaving to the left. At locations with higher volumes, higher speeds, or free-flow movements from the ramp to the roadway, a longer distance is required to safely make this maneuver. NCHRP Report 420 is one source of spacing guidelines (4-3). References 4-1. TRB Committee on Access Management. Access Management Manual. Transportation Research Board, National Research Council, Washington, DC (2003) 388 pp. 4-2. Koepke, F. J., and Levinson, H. R. NCHRP Report 348: Access Management Guidelines for Activity Centers. Transportation Research Board, National Research Council, Washington, DC (1992) 111 pp. 4-3. Gluck, J. S., Levinson, H. R., and Stover, V. G. NCHRP Report 420: Impacts of Access Management Techniques. Transportation Research Board, National Research Council, Washington, DC (1999) 157 pp. 4-4. Stover, V. G., and Koepke, F. J. Transportation and Land Development, 2nd edition. ITE (2002) 700 pp. 4-5. AASHTO. A Policy on Geometric Design of Highways and Streets. Washington, DC (2004) 896 pp.