2001-03-19 Special Called Regular Meeting and Public Hearing

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11 1", .. :. 106 I i It ., /., \' ! i ' i 'J 1}~ll uEw ~Oc;, PjCl-E f<r M R\ ~\)IL S rA~~l)' rt A~(V([} I ~ '.~ tot .' " "~ '.., - '>- -. ,po. .., l' .. l~" ~ ... ,~ l " I': ~I II" \: I! [' i ~! , I I , ' I 1\ '"7. , I I: : i ~ I i e (];) e Chap. 4 / Functional Circulation Systems Contrary to popular belief, the use of frontage roads is not a good technique to limit direct access to an arterial street in urban or developing urban areas. As shown in Figure 4-22, 64 major conflict points are created. When development occurs along the frontage roads, especially commercial development, the resulting traffic volumes result in congestion and accident potential as a result of the low-capacity, overlapping maneuver areas, close proximity of numerous conflict points, and the need for the driver to observe a large and poorly defined area. Location and Spacing No direct-access drive to an arterial should be located within the operational area of a signalized intersection. Short spacing between unsignalized access drives compounds the driving task by requiring the driver to watch for ingress and egress traffic at several points simultaneously while maintaining lateral and longitudinal control of the vehicle together with monitoring several vehicles ahead, behind, and in adjacent lanes. Longer spacings simplify the driving task by reducing the amount of information which must be simulta- neously acquired, processed. and reacted to and increasing the time between medial and marginal conflict points. Table 4-6 presents the access-drive spacing that is needed to eliminate overlap of the conflict areas created by a vehicle making a right turn from a driveway and entering the through traffic stream. Thus. it represents the minimum driveway spacing which allows the driver of a through vehicle to monitor one driveway at a time. rather than two or more simultaneously. As indicated by footnotes (b) and (c) to Table 4-6. notice that very high speed differentials will result even at relatively low speeds. Therefore. they should be interpreted as the minimum spacing at which adjacent access drives begin to function as independent intersections. Major and Buckley [18] have indicated that. from the standpoint of delay to vehicles entering the traffic stream and the ability of the traffic stream to absorb vehicles exiting from driveways. numerous driveways at close spacings result in delay and cause conflicts which increase the traffic hazard. On the other hand. d~iveways spaced at distances greater than 1.5 times the acceleration distance will reduce delay to vehicles entering the traffic stream and will improve the traffic-absorPtion characteristics of the traffic stream. Mini. ". j ~ t l ( .... . Figure 4.22 Conflict points with parallel frontage road.