Level of service and capacity of complex uncontrolled intersections – Development of an analytical estimation procedure (VSS2008/301)
Overview
Background & policy context:
Abroad, there is no available publicized process for assessing the performance and the traffic flow in uncontrolled nodes and places. Both the American Highway Capacity Manual (HCM) and the German manual for the design of road traffic systems (HBS) contain the same method as the Swiss VSS standard SN 640 022nd.
In order to answer questions about urban transport performance and traffic flow, an approach was developed in recent years by Pitzinger / SPACEK ("A new approach for estimating performance and traffic flow at uncontrolled intersections", Journal of "Traffic engineering", Issue 4, April 2007). Although this approach indeed proves to be useful in practice, it needs to be adapted and revised with each new assessed transport project. Furthermore, not all complex problems are addressed at urban landscaped nodes, and the approach is also based on too few representative benchmarks.
References:
Forschungsgesellschaft für das Strassen- und Verkehrswesen (FGSV): „Handbuch für die Bemessung von Strassenverkehrsanlagen (HBS)“, Köln 2001
PITZINGER P., SPACEK P.: „Ein neuer Ansatz zum Abschätzen von Leistungsfähigkeit und Verkehrsablauf an ungesteuerten Knotenpunkten“, Strassenverkehrstechnik Heft 4, April 2007
Schweizerischer Verband der Strassen- und Verkehrsfachleute (VSS): SN 640 022 „Leistungsfähigkeit, Verkehrsqualität, Belastbarkeit; Knoten ohne Lichtsignalanlagen“, Zürich, Mai 1999
Transportation Research Board (TRB): “Highway Capacity Manual (HCM 2000)”, National Research Council, Washington DC
Objectives:
The project had the following objectives:
- to develop an analytical estimation procedure to determine capacity, traffic flow and level of service of complex uncontrolled intersections; and
- to verify the elaborated estimation procedure on the basis of selected empirical measurements.
The project develops a procedure for estimation of capacity and traffic flows at complex uncontrolled intersections. Combinations of conflicts with pedestrians, vehicles, trams and buses are considered, with traffic participants in one lane and multiple lanes who have the right of way or yield, participants of higher and lower rank, and conflicts with shared lanes. Changes of the right of way at higher degrees of saturation are also considered. The procedure is applied on examples and results are being compared with measurements at existing intersections.
Methodology:
An analytic procedure is based on estimation of capacity and level of service at complex uncontrolled inter-sections. Inputs to the procedure are the geometrics of the intersection (lanes, shared lanes, flared ap-proaches with additional storage, tram and bus lanes and stops, assignment of right-of-way), the traffic vol-umes and queues for oversaturated conditions. Basics of the procedure are saturation flow rates for trams, buses, pedestrians and vehicles, and equations for delays and queues, accounting for random departures and arrivals and for oversaturation.
Capacity and level of service are then estimated for elements of uncontrolled intersections:
- for two-rank conflicts without or with changing of right-of-way
- for conflicts with upstream signals
- for conflicts with downstream congestion
- for multi-rank conflicts without or with changing of right-of-way
- for conflicts with parallel lanes
- for conflicts with shared lanes
- for uncontrolled conflicts at signalized intersections with permitted turning from exclusive lanes
- for uncontrolled conflicts at signalized intersections with permitted turning from shared lanes.
The analytic procedure is applied on examples - the elements of uncontrolled intersections are combined, capacity and level of service are estimated, compared with measurements, and the estimation is verified.
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