Thursday, January 29, 2004

Back on the Buses

As I have mentioned before, I commute to downtown Seattle using the King Country Metro buses. Over New Year, KC Metro took delivery of some new rolling stock. These new coaches can be distinguished from the older ones because they have a low floor and only a single step into the main cabin. The low floor is achieved by moving the engine to the back of the bus where it is mounted vertically. There is no rear window in a low floor bus. In addition, the wheel arches of the front wheels protrude into the passenger cabin. This reduces the seating capacity.

So here is the Theory of Constraints explanation as to why low floor buses make sense most of the time, but why they don’t always make sense on my oft traveled routes - no.18, no.15 and no.17.

As I explained before, the usage of a public transport system is dependent on the frequency of service and reliability of that service to run on-time. With a frequent service which is punctual, a virtuous cycle develops where travelers use the service more and come to depend on it more. As soon as either frequency or punctuality drop off, the passengers go looking for their car keys and a vicious cycle has started. So systems thinking and constraint thinking go hand-in-hand to provide an efficient public transport system.

Now for the constraint thinking! The new low floor buses provide ease of access for those with a mobility challenge such as elderly people. It is easier to get on and off a low floor bus. It is also faster for elderly people to get on and off when there are less steps. For those in a wheelchair or using a walker, they require use of the lift. When the floor is lower, coupled to a self-lowering suspension, the lift will extend faster. In fact I timed it as 30 seconds faster to load a passenger on a low floor bus. Again as I explained before, timeliness is important to the service. The bus will suffer variance in schedule as it travels through traffic. A big driver of variance is how many people get on or off and how quickly they can pay their fare. Elderly and disabled people increase the variance on stops - particularly when the lift is used. Providing low floor buses provides a win-win. It is better quality of service for those who need the benefits of a low floor and it helps reduce variance which helps to keep the buses running on-time!

So low floor buses are a boon! Right?

As I mentioned, the low floor design, reduces seating capacity. In fact at least 8 seats are removed by the intruding wheel arches and the vertically mounted engine. This is not a problem when capacity is not the constraint. When the constraint is purely adherence to timetable and the bus is under-utilized then it is never a problem that 8 seats are no longer present. However, the routes no.15 and 18 and to a lesser extent 17 were chosen to be replaced by the future monorail. The reason for this choice is that routes 15 and 18 are the most heavily used routes in the city. During rush hour, the 15 and 18 buses are capacity constrained. It is common for the standing room to be full and for passengers to be turned away. The introduction of the low floored coaches has only exacerbated this problem.

So how can this broken constraint be elevated? Clearly reducing quality of service for elderly and disabled passengers is not the answer. The truth is that the monorail replacement cannot come soon enough. The monorail will provide enough capacity and by elevating (literally) above the traffic, variance is reduced and adherence to timetable is no longer a concern. Roll on December 2007!!!