London’s tram service could get an extension southwards to Sutton as TfL opens a consultation into which of three routes it will build.

Three options are being considered that would link Sutton with either Wimbledon, South Wimbledon or Colliers Wood. It was announced last month that the consultation would open in October, so they’ve just about hit their deadline.

TfL is making it clear that they do not favour the Wimbledon link, as it would be delayed by Crossrail 2 construction, and can only be offered as a tram option. The Wimbledon option would also replace an existing railway line, so trams would replace trains on the Thameslink service.

For the other two routes, TfL is proposing either a tram service, or a Bus Rapid Transit (BRT) which is where the bus lane is physically separated from the rest of the road so that buses can run uninterrupted.

The possible BRT for the Sutton Link would be a ‘tram on rubber tyres’, with vehicles very different from the types currently used on the local bus network.

A key difference is that the BRT buses carry fewer passengers than Trams, so they would have to run the buses more often, leading to higher costs, and also more buses means regular interruptions to other road users.

Although constructing a tram route is more expensive initially, the operating cost over the long term could be lower as fewer vehicles and drivers would be needed.

Both route the Colliers Wood and South Wimbledon routes are expected to have similar costs. If delivered as a tram the cost of these options is currently estimated to cost in the region of £425 million, whereas BRT options for these routes are currently estimated to cost in the region of £275 million.

A planned second extension of the tram further south to the Royal Marsden Hospital site which is being promoted as a London Cancer Hub would cost an additional £100 million, if delivered as a tram service.

Funding is also uncertain, with the two affected councils providing £30 million, and TfL currently providing £70 million, but only through its Growth Fund, which then means any funding is dependent on there being commercial developers willing to pick up the rest of the bill.

Of the other two routes, the Colliers Wood option is unexpected, as all the talk about the extension over the past few years has been for a link from South Wimbledon.

Both could be either trams, or BRT, and both have pros and cons.

The South Wimbledon link seems to have the least impact on existing road traffic users, but the junction with the existing tram service at Morden Road is very tight and would make a future link with Wimbledon town centre harder to build.

The Colliers Wood option has problems with separating buses from cars along part of the route, but would make a future Sutton-Wimbledon link at Belgrave Walk easier to build.

The full details, plus the consultation and details of public exhibitions are here.

The earliest date that construction could start is in 2022 with services commencing not sooner than 2025.

Adding the tram to the tube map at either South Wimbledon will be fun for the map makers, working out how to include the Tram fare zone along the existing fares for the Northern line stations.