Sunday, 7 December 2014

A tram wreck in slow motion

 Only just... (from SMH)
Ms Berejiklian has confirmed that Alstom, one of the partners in the Connecting Sydney consortium, declined to manufacture nine or even seven segment trams and insisted on coupling two of its off-the-shelf five-segment trams to run through Randwick, Kensington, Surry Hills and along George Street to Circular Quay. The trams will be 67 metres long, 10 metres longer than a hypothetical nine-segment tram.

Tram driver's sightlines at Rawson Place stop
This of course has an unfortunate, um, knock on effect for passengers at the critical Rawson Place stop. The rear of a tram waiting to cross Pitt Street is 67 metres from where the driver of a following tram expects to stop and the driver has a negligible distance to react from where he first sights the stationary tram.

Ms Berejiklian refuses to say where the stops will actually be located citing Cabinet in Confidence but there is not much space to play around with. The Google Earth reconstruction above assumes the stationary tram is at the Pitt Street pedestrian crossing. We are told that trams will have priority signalling and will be travelling at the speed limit between stops. Indeed there is not much reason for trams to not have priority signalling between the Chinatown and Rawson Place stops - no major cross roads. This is the only place in the CBD where trams can pick up time. Vehicles waiting in the single general-vehicle lane and buses waiting to pass through the pincher movement of death block the driver's view until he is entering the intersection, with priority signalling. When he first glimpses the stationary tram he is less than 34 metres from impact. Travelling at 50 kph he has less that 2.5 seconds to impact, probably less than his reaction time.

Coupled carriages have a tendency to jack-knife on impact so the trams would cut a swathe through pedestrians waiting dutifully at the aptly-named pincer movement. In fact, the carriages will unavoidably jack-knife on impact. The second 33 metre long carriage is just at the start of the curve in the tracks when the first carriage plows into the stationary tram. The momentum of the second carriage will propel it south overturning the first carriage and taking out a tram headed north into George Street in parallel during the priority signal phase. The momentum of the second carriage of this tram will propel it west overturning the first carriage onto vehicles travelling north along George Street at the speed limit in parallel with the tram movements. Vehicles approaching the intersection at the speed limit will plow into trams and vehicles strewn across George Street or be deflected into pedestrians and buildings on the western side of George Street.

Transdev Sydney, a minor bus operator in south-west and outer western Sydney and lead partner in the Connecting Sydney consortium, will file for bankruptcy. The NSW taxpayer will pick up the pieces.

The Capacity Improvement Plan

The Sydney City Centre Capacity Improvement Plan, on exhibition until 9 January 2015, allows us to make an assessment of the spacing between trams that would be necessary to avoid a catastrophe that would lead news bulletins across the globe. It turns out that the improvements that are mooted achieve laughable increases in traffic flows to offset the very large degradations in road capacity brought about by the George Street trams.

The main efforts have been to increase east-west traffic flows. All parking is removed from King Street, dumping more vehicles into the mother of all pinch points, and pavements are reduced in width in Market Street. It should be pointed out that most of the vehicles that traverse the full length of King Street could use the Cross City Tunnel but choose to not pay the toll.

Goulburn/George Street intersection
Goulburn Street changes from a six-lane road to four lanes west of George Street. Goulburn Street west grid-locks every evening. Sydney City Council has tried to slow traffic by forcing left-turns to be made from the through-traffic lane. The don't-walk sign comes on after 25 seconds between 20 and 30 seconds before the orange light comes on during the evening peak. The State Government is demanding that a left-turn lane be re-established. That's the only change. The pedestrianisation of George Street will increase the volumes of traffic needing to make this turn.

Wentworth Avenue - Capacity Improvement Plan
Wentworth Avenue is coloured pink signifying vast changes but the only changes are from the elimination of some parking an the establishment of clearways.

Market Street changes
The brochure concludes: "only a limited amount of traffic capacity needs introducing along Market Street as there are other capacity restraints preventing its use". Vast changes to the pavements adjacent to the QVB are proposed but the number of lanes crossing George Street remains at three. A left-turn lane into York Street would stretch the whole block but delivers vehicles only to the carpark under York Street as at present. Vehicles exit from the car park into Druitt Street, creating no end of problems for bus services from the Harbour Bridge that will foolishly be terminated at Druitt Street and for bus services from Victoria Road sent on through to terminate God knows where in the Eastern Suburbs, i.e. Edgecliff station.

The destruction of capacity

The destruction of capacity in the CBD south of Bathurst Street has been documented in the exhibited and the never-exhibited EIS for CSELR and the Sydney City Centre Bus Infrastructure brochure:
  • George Street capacity halved to one lane south of Bathurst Street;
  • Bus lanes removed from Elizabeth Street south of Foveaux Street;
  • Through traffic in Foveaux Street halved to one lane;
  • Southbound traffic capacity in Elizabeth Street halved to one lane at Park Street.

Returning to George Street with a vengeance

Every vehicle in George Street north of Park Street is there for a purpose - George Street is not a thoroughfare. Vehicles displaced by the pedestrianisation of George Street must return from whence they came. The likely routes are from Castlereagh Street returning to George Street via Liverpool Street and Goulburn Street. But the capacity of George Street has been halved.

The intersections of George Street with Bathurst, Liverpool and Goulburn Streets are operating at above capacity every evening and are under the control of SCATS. The closure of Rawson Place will divert additional loads on the east-west roads but the south-bound traffic will only increase in accordance with the addition of off-street parking in the northern CBD. This is under the control of the Sydney City Council and can be predicted. The most significant changes to the traffic flows through the intersections is from the halving of capacity in George Street. Once an intersection is operating above capacity the only thing that will change over time is the period of time during the day when traffic is being delayed.

One cannot surmise on how SCATS will respond to the reduced capacity in George Street. It could lengthen the phase for George Street flows or cycle the combined phases more frequently. Buses queued in the bus lane clear the intersection well before the phase is finished and even 67 metre trams would not be the determinant factor in the phasing. The pedestrian crossings are the major factor in the phasing of traffic lights in Eddy Avenue.

One can safely predict that the phases for east-west traffic movements across George Street will increase in duration with the introduction of trams. The location of the tram stops insures that the delays at the intersections are cumulative. Trams stop at every stop and cannot take advantage of the looping by SCATS of the lights at Bathurst Street and Liverpool Street intersections.

Not all vehicles would return to George Street, some would turn south into Pitt Street, inexorably crossing Eddy Avenue. This is the intersection that sets up the stationary tram for catastrophe. The southbound phase for this intersection is the minimum time needed for pedestrians to cross in the mornings but increases during the pm peak periods leading eventually to SCATS taking over the timing.

I tallied up the cumulative delays for trams at the intersections at Pitt Street, Goulburn Street, Liverpool Street and Bathurst Street in a previous post SCATS assault from the North Shore rump. This was assuming that trams would get priority at signals between the Chinatown and Rawson Place stops. One can make no assumptions as the whether the trams would have priority at the few intersections across the pedestrianised zone: Druitt Street, Market Street, King Street and one-lane-each-way Hunter Street. Since these crossings have limited capacity and are congested for most of the day it would seem foolish to give priority to 67 metre trams travelling at little more than pedestrian speed - taking into account the experience of the trams in Sydney's world-class pedestrian concourse outside Paddy's Market and the trams in Melbourne's CBD. Trams in the Melbourne CBD travel slowly (10 kph) with a clear view of the tram ahead and they are never coupled together.

The current delays at the SCATS controlled intersections on average were 1 minute 20 seconds at Pitt Street, 40 seconds at Bathurst and Liverpool Streets and 50 seconds at Goulburn Street, a cumulative 3 and a half minutes. To this you must add the time spent at the Rawson Place stop picking up passengers to get the minimum period between the dispatching of trams needed to avoid a tram being run down. To be on the safe side you would be looking at a frequency of no more than one tram every 5 minutes and greater if there is not priority for trams at crossings in the pedestrianised zone.

This is the maximum possible frequency for the trams from day one and the frequency gets progressively less over the remaining life of the City of Sydney.

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