Cambridge likes to style itself as a place where ideas are formed. “Cambridge ideas change the world,” according to the university.

And the city is currently having a lot of ideas about how to solve its traffic problems. The region’s metro mayor, James Palmer, is on record as supporting the idea of an underground rapid transit system for the city. Local campaign groups, business lobbyists and professors alike have weighed in with their ideas, and sketched out exciting maps of future transport systems.

But while the city supports copious innovation in electronics and biotech, it absolutely should not be trying to innovate in public transport.

Here’s why: Cambridge is really small for a city. The 2011 census put its population at 123,000, but the city is growing, so it’s perhaps 130,000 now. The current record holder for “smallest city with a metro system” is Lausanne, Switzerland – population: 146,000, but in an urban area of 400,000 – which has a light rail line and an underground metro line. The latter is less than four miles long, and cost around half a billion pounds to build when it opened in 2008. It’s also on a really steep hill: the metro allows people to easily travel between the upper and lower parts of the city. This is definitely not a problem that Cambridge has.

So, what could we do for Cambridge? Lots of people argue for trams. They’re fast, quiet, give a smoother ride than a bus, and the fixed infrastructure means that they raise property prices along their route, which can help with financing them.

For such a system to work properly, however, you’ve got to give it a dedicated route – or the trams will get just as stuck in traffic as the buses already are. That means closing a lot of roads in the city to cars, in order to make space for public transport.

Given we can’t find enough street space to give priority for buses on the roads into the city, it’ll be just as difficult for trams. Even worse: tram tracks are really not kind to cyclists. In a city where 29 per cent of the population cycles to or from work, disrupting cycling is going to be really counterproductive.

The “Isaac Newton Line” – a massive proposed light rail system with four underground stations in the city, with options to be extended all over the region (click to expand). If only money grew on trees. Image: CambridgeConnect.

“But wait,” say various armchair engineers, “we could have a tunnel!”

That’s true. We could have tunnels for trams in the city centre, and run them on the surface further out.

Now you’ve got a tram system with underground stations, so that’s more expensive to build, and also more expensive to operate (because underground stations are likely to need to be staffed for safety).  You’ve also got to work out where to put the portals.

Another Cambridge – the one in Massachusetts – has a tunnel for its trolleybuses, to allow passengers to interchange easily with the underground metro at Harvard Square. The ramps to the tunnel – which is only just below the road surface – are 100m long. If you wanted a tunnel under Cambridge, UK, you’d end up doing some serious demolition to make enough space.

 

The Harvard bus tunnel in Cambridge, MA: the northern approach ramp runs through a park, and the southern one is underneath the One Brattle Square shopping complex. Both require a strip about 100m long. Image: Open Street Map.

“Can’t we have a more innovative solution?” Well, step forward the Affordable Very Rapid Transit, or AVRT. This is the brainchild of John Miles, a professor of civil engineering.

He proposes a wheel-shaped network of tunnels, with a single central underground station, and connections to a series of sites around the periphery.

AVRT: here’s a sexy computer rendering of a non-existent eight-wheeled autonomous bus. Image: Connecting Cambridgeshire.

To save money, the tunnels will be single-track, with driverless vehicles shuttling back and forth between stations at each end. Passengers will be required to change at every station – because this will save on the cost of the signalling.

A map of the AVRT proposal: click to expand. Each of the blue lines is a tunnel served by vehicles shuttling back and forth, with no through connections. That central underground station is going to be an overcrowding nightmare as everyone tries to change between four different routes all at once. Image: Smart Cambridge.

Miles’ reports (vol. 1  and vol. 2 ) read a lot like he’s trying to reinvent the wheel from first principles. Many aspects of his design resemble the now-30-year-old Lille Metro, which isn’t even referenced.

There’s a very good reason why Cambridge should not spend any further public money on such schemes. There’s one thing guaranteed to be more risky and expensive than a new rapid transit system – and that’s a new rapid transit system based on entirely novel and untested technology.

Cambridge is simply too small to take the risk. It’s already been burned by the Cambridgeshire Guided Busway, another grand experiment that ended up taking longer, costing more,  and looking like it’s going to be more expensive to maintain than previously thought.

So what should the city do? For a fraction of the cost of rapid transit, Cambridge could:

  • Build more segregated cycle lanes and cycle routes;
  • Use the mayor’s powers to take control of the local bus franchise, and give it sensible unified ticketing;
  • Extend frequent bus routes out to the surrounding villages, and reduce their dependence on park and ride and city centre parking;
  • Fund electric or hybrid buses to reduce noise and air pollution in the city;
  • Fund improvements to the rural heavy rail lines, giving a higher frequency service to nearby towns like Newmarket.

It’s not as exciting – but it’s much lower risk and much higher reward. Cambridge may be the best place to innovate for many industries, but public transport definitely should not be one of them.

Mike Prior-Jones is a Cambridge-based engineer.

Why not read these related articles? Are trams really better than buses? What is bus rapid transit – and why doesn’t every city want one?