Annex 12 Traffic Management

The implementation of busways, which reserves part of the carriageway for buses only, inevitably has some impact on the free movement or available capacity of the remaining carriageway for other modes. However, at policy level, this may be considered to be the reason for the busway: to make bus operations more attractive than other modes. Whilst the total passenger throughput can be maintained or even increased through improved bus operations and there will be some benefit to mixed traffic from the removal of buses from the mixed traffic lanes, the system much depends on achieving modal diversion away from private vehicles and designing appropriate traffic management measures to ameliorate impacts.

The implementation of a busway will impact upon the transport network in terms of junction and link capacity. It is important to note that in urban and semi-urban conditions, the capacity constraints of intersections are most likely to have the greatest constraining effect. Therefore, the planning of HCBRT should include consideration of the impact on other traffic and appropriate traffic management, particularly for the design of intersections.

Impact of Busways on Carriageway Capacity

It is fundamentally important to assess whether traffic flow can operate within link capacity, so that subsequently implementing traffic management methods at intersections is a worthwhile and viable action. Ideally, the basic questions in the box below should be answered when considering impact of BRT on link capacity, though a quantified assessment can only be made through detailed network modeling. Cities, such as Bogota, Colombia, have shown that such modeling in combination with passenger forecasts can later be a crucial element in not only designing system capacity, but also attracting the private sector to absorb demand risk and make appropriate investments in the proposed system.

Questions for Assessing Impact of BRT Facilities on Other Modes

  • What is the existing flow/capacity on the roads proposed for busway implementation?
  • What is the loss in capacity of the carriageway remaining for non-BRT modes following busway implementation?
  • Is the remaining carriageway still capable of handling existing and future private traffic?
  • Is the entire corridor (all modes including BRT) capable of handling the overall trip-making demand (throughput)?

The final question is particularly important as it relates to transport system capacity and whether or not appropriate policy-making can contribute to an efficient network, i.e. even if private trip-making is compromised, there is still the means to make the desired trip.

Carriageway capacity can be improved by applying basic traffic management techniques including parking regulations and enforcement, improving the capacity of parallel roads, regulations on vendor activity, and reducing the width of medians.

Traffic Management at Intersections

Intersections may be designed to provide priority for BRT vehicles at any cost to other traffic or to ameliorate the impact of mixed use. Proving a dedicated turning late for BRT vehicles maintains the buses within the segregated network, which may be an important consideration for the image of the system, but physical space to accommodate an additional turning lane is necessary. Providing a queue jumping facility to give buses a head start at intersections will cause delay to private modes.

In order to assess the impact of busways on intersections, an analysis of each junction within the BRT route would typically be required. Some constraint to private vehicle flow is likely to be imposed due to priority of buses at junctions. However, a BRT scheme should also aim to improve overall traffic management through the organization and rationalisation of all traffic modes. While there could be a small reduction in intersection capacity for non-bus traffic, this should be offset by improved traffic management for all traffic including methods such as improved traffic signal phasing to minimise conflicts and optimise clearance times, and physical junction channelisation islands to steer vehicles into clear and direct paths through junctions.

Specifically, the impact of BRT on other vehicles at intersections can be directly ameliorated by traffic management measures, such as those listed below.

  • Redistribution of other modes to routes away from bus priority routes;
  • Maximising capacity of carriageway near the intersection by removal of bus stops from the kerbside, closing of U-turns and rationalisation of side access roads;
  • Improved traffic signal phasing to minimise conflicts and rationalise clearance times;
  • Management of right turning traffic by various options:
    • simultaneous non-hooking right turn signal phases
    • designing P or G turns whereby right turning traffic turns left either before or after the junction, loops round and crosses the junction with traffic on the opposing phase (relies on the density of the secondary road network);
    • banning some turning movements such as right turns at the intersection;
    • allowing the BRT vehicle to turn at a smaller junction prior to the main intersection and use the secondary road network;
    • physical junction channelisation islands to steer vehicles into clear and direct paths through junctions and bringing stop lines forward to reduce clearance times;
    • grade separation (flyovers and underpasses that may be either dedicated to the use of BRT buses or for other traffic thereby decongesting the intersection)
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