[thedoc (OP)]

Clive Boothby asked the Naked Scientists:
   Many towns and cities had trams which are now returning, and some were replaced by trolley buses, which surely are better for the environment. But why were the trolley buses scrapped?
What do you think?

[alancalverd]

Good point. I am impressed by the Manchester tram system which exploits old railway connections to the suburbs and nearby towns, thus offsetting the aggravation of tramlines in the inner city by the convenience and minimal environmental impact of smooth integration with an existing, rational  transport system. But AFAIK the Edinburgh and Sheffield trams, and the infamous Cambridge Guided Busway, are just examples of civic lunacy and financial corruption.

Running steel on steel is inherently noisier and demands a greater unsprung weight than rubber tyres on tarmac, but the weight penalty  might be offset by the reduced environmental impact and general inconvenience if a suburban tram could convert to a rubber-tyred trolleybus in town. 

[SeanB]

Mostly the impact will be lower, as the power is not generated on board by a poor efficiency diesel engine. Poor efficiency as it is small, has to be light mass and compact. A larger power plant that has less restraint on size means it will be able to convert fuel to usable power more efficiently, and bigger here is going to be more efficient just from there being value in shaving every last bit of efficiency out of the cycle. Yes, you do have transmission losses, but these are lower than the loss in the existing diesel drivetrain, and with a decent electronic control you can recover a lot of power during braking to use to power other units on the same grid line.

Major disadvantage is that you have to have brass bars to distribute power, and for trams limited ability of being able to route lines due to gradients and you need special passing areas for them. Needs a lot more initial infrastructure cost and design than a standard road, but if you have trams you can use existing roadways with the light rail cars having a section, and other traffic having to give right of way.

[syhprum]

When I was a boy we had a trolley bus system in Maidstone powered by a 20 megawatt coal fired power station in the center of the town, the environmental impact was considerable !

[alancalverd]

That's the whole point of electric transport - separate the pollution from the user. Doesn't get rid of pollution but means you have pollution in one place and congestion in another. A misery shared is a misery doubled.   

[Don_1]

That's the whole point of electric transport - separate the pollution from the user. Doesn't get rid of pollution but means you have pollution in one place and congestion in another. A misery shared is a misery doubled.   

Quite so Alan. Electric vehicles will only become 'clean', or at least fuel clean, when the power is generated by clean means.

But getting back to the trolley bus, being an old git, I still remember the LT route 96 from Woolwich to Dartford using trolley buses. Though they had the advantage of running on roadways which could be shared by other vehicles, they suffered from one seemingly insurmountable problem.

The trolley bus had to get its power from overhead cables via long pick-up arms mounted on the roof.


Image - Ben Brooksbank

In order to avoid catastrophic electrocution in the event of an accident, these pick-up arms had to be able to disengage easily from the overhead cables, so as not to drag live cables down on to the bus, or other vehicles, pedestrians etc., in the vicinity.

But if the driver were to stray beyond the parameters of the pick-up arms or there were a sharp jolt, the pick-up arms could disengage mid journey and maybe in the middle of the road, leaving the bus stranded.

Well I remember how, on the old 96, this was a common occurrence, particularly at Welling Corner. Come rain, wind, snow or shine, the poor old bus conductor had to get the long pole out from under the bus and struggle to re-connect the dropped arm.

[alancalverd]

The tram pickup, using a single wire and a wide pantograph wiper, certainly seems more reliable. So here's an alternative: a single overhead wire and a flat earth strip, but only on certain sectors of the route. Now we have a battery driven bus that can weave around the traffic like a diesel, but can recharge on straight sectors or occasional dedicated bus lanes.

Come to think of it, the longest London bus route is only 26 miles, so why not use battery-powered buses that recharge at the end of the route? Even the G-Wizz can cover more than 40 miles on a charge, and modern electric vehicles are supposed to have much greater ranges. IIRC the old trolley buses had an emergency battery, so why not have an emergency diesel engine that would just allow an empty electric bus to limp home if the battery dies?