PB was commissioned to test the operational robustness of Auckland’s Central Transit Corridor (CTC) to ensure that the proposed concept design would meet the medium-term and longer-term transit and operational needs in a city experiencing significant ridership growth. The greater Auckland region is home to approximately 1.1 million residents and is served by a fleet of almost 800 buses.

This high-capacity road-based transitway is planned as part of a general upgrading of public transport infrastructure. If it proceeds, it will link Auckland City’s downtown area with Newmarket, a major regional commercial and retail centre some 4.5 km (2.7 miles) to the southeast.

Table 1: Hourly Service Frequencies for Route Groupings

Table 2: CTC Bus Passenger Movements at Each Station in 2011: 2-Hour Morning Peak Period

Figure 1: Vehicle movements through stations — Scenario B (10-second threshold and calculated boarding dwell time).

Figure 2: Passenger demand and loadings, 2011 (bus only).

Table 3: Estimate of Station Blockages-Scenario B (Bus 2011) and Scenario C (Bus and LRV 2011)

Figure 3: Vehicle movements through Sheraton Station - Scenario C (10-second threshold and calculated boarding dwell time).

Figure 4: Passenger demand and loading 2001 (bus and LRV).

The Proposal

The CTC would be developed in two stages:

• Stage 1: A bus-only semi-exclusive kerbside transit lane serving seven stations. Each station would be a single kerbside platform 55 m (172 feet) in length. Upon entering the transitway, buses would generally remain in the transit lanes. Other vehicles would be permitted to cross the transitway or to enter it to access properties or for a “next turn left” arrangement.
• Stage 2: A light rail vehicle (LRV) or rubber-tyred rapid transit and bus operation in an exclusive median-based transitway. Upon entering the transitway both buses and LRVs would remain on the transitway for its entire length.

The Challenge

Our challenge was to demonstrate to the client the capacity of the transitway and its seven stations and their ability to operate effectively, given a range of future service frequencies, stopping patterns and mixed modal operating conditions. In conjunction with Interdynamics Pty Ltd, we used the Busway Interdyne simulation model to address our client’s needs. Our three broad tasks were to:

• Develop a bus operating strategy for the CTC
• Generate indicative bus numbers on the CTC in 2006 and 2011 to allow the operation of the CTC to be modelled
• Undertake simulation modelling of the CTC under a range of operating conditions and report on the adequacy of the transitway to accommodate future operational limits.

The Busway Interdyne Model

The Busways InterDyne^{TM 1} was developed to:

• Simulate transit vehicle movements through the alignment and stations under different operating scenarios (e.g. priority, no priority, kerbside and median running)
• Determine the capacity of the transitway to function at a future time through the three key performance indicators (KPIs) of transitway travel time, station blockages and passenger uplift capacity.

Through the simulation of vehicle movements, the model is able to inform the user when the volume and/or mix of vehicles through any station on the transitway would cause delays, when these delays would cause a temporary blockage to the transitway through lanes, the time of each delay, and the impact of these delays on overall transitway travel times. Passenger demand levels can be included (as was the case here) to determine, firstly, whether service levels are adequate to meet the passenger demand forecasts and, secondly, whether the transitway can accommodate the high service frequencies, different bus stopping patterns along the transitway and the mixing of bus and rail-based passenger transport modes.

Network Details. A total of 18 bus route groupings were restructured to serve the transitway. Table 1 shows the hourly service frequencies and Table 2 lists the 2011 targeted passenger demand for each station on the transitway in the morning peak period.

Three Scenarios. We examined three operating scenarios:

• Scenario A: A partially complete transitway operating in 2006 in an arrangement essentially the same as at present.
• Scenario B: A 2011 fully functional kerbside rapid bus transitway with all seven stations fully functional and the service levels and passenger demands as per the above tables.
• Scenario C: A 2011 median-based transitway operating on a segregated right of way with co-located high-frequency buses and LRVs.

Vehicle movements along the transitway were modelled under a range of permissible dwell times at stations to accommodate passenger boarding requirements, acceleration, deceleration, and safe operating protocols at intersections and through transitway stations. In essence, the simulation replicated real-life conditions.

The Study Results

The three KPIs of transitway blockages, passenger carrying capacity and total transitway travel times determined whether the transitway and station layouts would be able to cope with future operational and passenger demands. Scenario A was considered to be only a temporary arrangement so it is not reported in this article, although it was reported upon in the study.

Scenario B. Vehicle movements through stations are shown in Figure 1. The relevant transitway blockage count, given a set blockage setting (i.e., the time threshold before the model records a blockage), and the average station dwell time for passenger set-down and pickup are shown in Table 3. At these settings, we calculated the total demand and average load per bus through the peak periods (Figure 2).

Transitway travel times ranged from a low of 9 minutes when priority and minimum station dwell times were modelled. With no priority, the transit time extended to 17 minutes. If a 60-second dwell time was allocated to each station, the transitway travel time extended to 24 minutes. These KPI results confirmed that the transitway was operating at levels in excess of its capacity.

Scenario C. The KPI results for this scenario were slightly worse than for Scenario B, a result that was due partly to the introduction of the LRV mode with different acceleration and deceleration rates to buses, different station dwell times and different station operating protocols. The same bus service frequency and service patterns were used for Scenario C as for Scenario B.

Table 3 shows the transitway station blockages for this scenario. As can be seen, the transitway is operating at a level in excess of its capacity. Service levels were in excess of those required for the estimated passenger demands (Figure 3).
The final KPI, transitway travel time, ranged from 8 minutes to 35 minutes, depending on whether the station dwell time per bus was 25 seconds or 60 seconds. This result demonstrates that the transitway operation is very unstable at these frequencies.

A substantial reduction (approximately 50 percent) in service frequencies is required to ensure that the transitway functions adequately. Alternatively, a major redesign of the planning concepts would be required to increase the operational capacity of the transitway. Auckland City Council is currently considering the implications of this advice.