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Does the "guided bus" really have a purpose in life?
That question is increasingly being asked by many transit agency planners and decisionmakers, particularly in light of the recent experience of the transit authority in Nancy, a small city in the eastern Lorraine region of France, which in March 2001 was forced to shut down its brandnew guided-bus "tram on tires" system just one month after startup (and to provide substitute service with regular transit buses). Nancy's troubles highlight issues and serious problems with "guided bus" technology in general.
In the USA, where "rubber-tire" zealots seem to be waging a desperate and bitter battle against light rail transit (LRT), "guided bus" technology – in effect, the flagship of the "Bus Rapid Transit" (BRT) campaign – is being brandished as a cut-rate "train on rubber tires", an alternative which supposedly is "just like LRT, but cheaper", whereby the attributes of the low-cost, mass-produced bus are combined with various means of automatic vehicle guidance (such as small guidance wheels running against side curbs, or central guide wheels contacting an underground guidance rail through a slot in the middle of the bus's paveway).
In Europe, where a tiny handful of cities have opted for "guided bus" systems, the interest seems more in getting the "effect" of a tramway (streetcar) – in other words, installing a "pseudo-LRT" system with extra-long, multi-jointed buses camouflaged as streetcar-like vehicles with LRT body styling. in France, where new systems designated as TCSP (Transport en Commune en Site Propre – Segregated Surface Transit) are beneficiaries of a vigorous government funding program, most cities designating projects have selected LRT as their preferred mode – such as Grenoble, Nantes, Strasbourg, Rouen, Lyon, Montpelier, Orleans. But a few have opted instead for this or that "guided bus" scheme, mainly goaded by politicians jumping at what they think is the chance to install a "tramway at half price".
Nancy selects "guided-bus" BRT
That's essentially what seems to have been the case in the French city of
Nancy (pop. 255,000), which chose a "guided-bus" system as a way to
upgrade its existing 30-km (18.6-mi) electric trolleybus system. Nancy
selected a new, "sexier" bus "tramway" called TVR (Transport sur Voie
Reservé) being marketed by the Canadian firm Bombardier (a
transportation-industry giant which makes everything from motorized sleds
and jet skis to buses, railcars, and monorail systems). Nancy thus opted
for one of the most ambitious high-tech BRT installations in the world.
Unlike most other "guided-bus"
schemes, which rely on side curbs to contact small horizontal guide wheels of rubber on the bus, Bombardier's TVR uses
flanged metallic wheels on steerage mechanisms beneath the bus accessing a central, underground guidance rail via a
slot in the middle of the paveway (or "guideway"). From a central point on the underside of the vehicle, a pair of in-line small double-flanged
wheels are held down against the central slot rail by hydraulic force. The buses themselves are quite long – 24.5 meters (about 80 ft.) – with 2 bendable joints or "articulations" forming a 3-unit giant of a bus, with extra
double-width doors, 40 seats, and total capacity approaching that of an
LRT car. On top of this, Bombardier fitted a sleek body styled quite like a
true tram or light rail vehicle – not so hard to do, since Bombardier also
makes LRT rolling stock. There are several doors on one side, facilitating faster boarding/exiting of passengers.
The company have aggressively marketed their elongated bus as a "tram on tires", and Nancy's transit agency have maintained the strategy by calling their fancified bus system a "tramway". Of considerable assistance in the "tramway" project was the fact that much of the route was already (a) electrified and (b) located in reserved lanes or other segregated rights-of-way. Bus stops have been upgraded, for the most part, into small stations resembling those of LRT.
At a cost of 772 million francs (excluding vehicles) – about $108 million –
construction of Nancy's initial 11-km (6.8-mi) TVR Line 1 comes out at
about $9.6 mn per kilometer, or about $15.5 mn a mile. While that's
relatively cheap compared with a typical US higher-speed, "interurban"-style LRT system (like those in Denver, Salt Lake City, Dallas, St. Louis,
Portland, etc.), it's surprisingly close to the cost of an LRT streetcar
system, such as the Portland Streetcar (about $18.0 mn/mile). And, since
each TVR bus has a maximum speed of only 70 kph (about 43 mph), a
streetcar-type LRT – not an interurban, commuter-type operation – is
exactly what the TVR "tramway on tires" is positioned to compete with.
(Curiously, the TVR double-articulated bus weighs 25.5 metric tons
more than the Skoda LRT streetcar for Portland, which weighs 24.2 metric tons.)
"Guided bus" rationale
But if the installation cost of a "guided bus" operation is virtually equivalent to that of an LRT streetcar, what's the advantage? That's precisely what many LRT proponents are asking, leading some to characterize the so-called "guided bus" as ... a "misguided bus"! After all, for about the same capital expense, the "guided bus" does not hold great promise for lowering operating costs like LRT – even multi-articulated buses aren't as large as LRT cars, nor can they be entrained to minimize peak labor costs.
One of the factors that seems to be motivating interest in "guided-bus" technology is the problem of keeping a bus within a narrow pavement (paveway) width, particularly at higher speeds. A "guided-bus" route can be fitted into a narrower alignment profile, since such buses don't require the clearances needed for manually steered buses.
The clearance problem is most perceptible as buses approach each other at higher speeds. Drivers instinctively want to veer away from the middle; thus an ordinary (unguided) bus lane or busway must allow adequate clearances for this. Particularly in street lanes and narrow one-way route sections (e.g., narrow streets of older cities), LRT has the advantage of positive guidance (flanged wheels on rails) while manually steered buses may "stray" left or right while in motion because of the inaccuracies of driver judgement. This situation seems to be a major factor motivating attempts to emulate LRT guidance with various bus-guidance schemes.
While "guided-bus" technology has seen relatively little deployment to date, the most common system appears to be the curb (British "kerb") type of guidance (with small horizontal guidance wheels contacting a raised curb on each side of the paveway – thus it's also called KGB, for Kerb Guided Bus). Such buses seem to be capable of achieving higher speeds than those that use a center rail of some kind beneath the pavement (such as the Nancy system). in Adelaide, such curb-guided buses achieve 100 kph (about 62 mph) maximum operating speed.
Factors behind Nancy's decision
So, if it works so well, why are "guided-bus" developers and proponents looking for a better form of bus guidance? it turns out that the KGB system appears to have major complications. Wherever there are grade crossings or intersections, there must be a kind of funnel at each end of each curb to "collect" the guidance wheels and direct them into the proper alignment against the curb as it "reappears". Not only does this compromise reliability at high speeds (fortunately, Adelaide's higher-speed alignment has no grade crossings), but it also makes routing through city centers very cumbersome (since streets have to be fitted with the special guidance curbs).
Thus, Nancy opted for Bombardier's central-slot system with its underground guidance rail, apparently lured by the appeal of a guidance system flush with the pavement (similar to LRT tracks, which are routinely embedded in street pavement). Clearly appealing also was Bombardier's tramlike styling for its buses, which, with double articulations, are also longer than the common articulated bus. Evidently, the axle-mounted guidance mechanism helped keep the entire complex vehicle properly guided, from front to end.
Compared with LRT, the rubber-tired TVR bus "tramway" does have an advantage negotiating a very steep 13% grade in one section of Nancy's route system. in addition, the new TVR buses have 2 trolley poles, enabling them to readily use the existing 2-wire overhead contact system (OCS) of Nancy's electric trolleybus system. (LRT uses only a single wire, since electric current is returned via the steel railway tracks themselves.) Another important advantage of the TVR system is its ability to operate on unelectrified streets "beyond the wires" – already a feature of Nancy's trolleybuses, which carry onboard diesel generators.
However, by 1998 the specialized hybrid trolleybus vehicles were becoming increasingly unreliable, with replacements and spares harder to procure. Thus, when Bombardier salesmen came knocking, Nancy planners perceived an opportunity to preserve the investment in their system infrastructure while upgrading to supposedly LRT-like performance with Bombardier's TVR guided trolleybus system.
Evidently, for Nancy's planners and decisionmakers, LRT's potential for lowering operating costs by running longer vehicles and coupling them in trains held no appeal. Nor were Nancy planners apparently daunted by leaping into a basically new and relatively untested, proprietary system, thus probably locking themselves into a single vendor for future rolling stock.
Nancy races ahead ... Into trouble
Hence, Nancy transit management plunged ahead to embrace the TVR "guided-bus" system, assuring a skeptical public they were shrewdly acquiring LRT performance at a fraction of the cost, while LRT proponents questioned why they would go to 85-90% of the capital expense of LRT to get none of its cost-cutting, capacity, and other advantages. (Actually, since only about 8.6 km – 5.3 mi – are guided, the cost for the guided alignment of Line 1 comes out to $20.4 million per mile, higher than the cost of Portland's LRT streetcar line, and closer to the cost of a US higher-speed interurban-style LRT system!)
But for all their clever parsimony, Nancy transit managers begin encountering snags almost from the start. The problems of installing an unfamiliar infrastructure and deploying the first production batch of a unique type of vehicle took their toll. Planned opening dates in December 2000 and January 2001 were missed as "teething troubles" kept cropping up.
Finally, on 11 February 2001, Nancy became the first French city to initiate the TVR "tramway on tires" system, opening its Line 1 to revenue service. At last, Nancy could claim that it, too, had its "tramway" ... and at a bargain price! So what if critics argued they had paid about as much as the cost of a steel-wheel LRT tramway for an unconventional, proprietary system limited in capacity? And that they would probably have less money for expansion because of higher operating costs? And that the public probably wouldn't be fooled that they had more than a fancier bus system? The TVR was different, it was supposedly "flexible", and it seemed to provide a "tramway" cachet on the cheap.
"Misguided" buses ... literally
But much bigger problems soon emerged. With allegations flying that the
vehicles did not meet safety criteria, and complaints about the noise
generated by their operation, the TVR "tram on tires" became an election
issue. The situation soon got a lot worse. On 6 March, at a point where
Line 1 route transforms from guided to unguided mode (Essey), one of the
TVR pseudo-LRT buses lost stability, causing its rear end to strike a
power-line pole, and injuring three passengers with flying glass. The
drivers then went on a one-day strike on the grounds that the new system
was unsafe. No sooner had they been coaxed back to work, when exactly
the same thing happened at the same point on 10 March, fortunately at
05:50 (5:50 AM) in the morning, so there were no injuries. The line was
shut down immediately and indefinitely pending an inquiry to be held by a
It turns out that a similar incident had occurred on a TVR test system
running in Paris (where a TVR guide rail had been installed on 1.5 km of
the 12-km Trans Val-du-Marne busway) in the spring of 2000. A witness
described the bus's rear end as behaving "like a scorpion's tail", with only
good fortune preventing contact with anything solid. That incident
appears not to have been publicized – indeed, news of it may have been
hushed up – but it now seems clear that there is an inherent instability to
the rear section of a TVR vehicle, possibly triggered by certain conditions.
"The Bombardier engineers must be worried people" observes Mike
Taplin of the Light Rail Transit Association.
"Guided bus" vs. LRT
While the Nancy "rubber tramway" system has been shut down for the moment, with conventional bus service apparently substituted, one can expect that Bombardier will eventually get it up and running in some fashion – engineers are clever and persistent people. But that still leaves the question hanging: Does the "guided bus" (or "misguided bus", as the case may be) truly have a viable purpose in public transit? On what deficiency of LRT does it improve?
The "low cost" frequently claimed for busways, including "guided bus" systems, may be misleading. in Nancy, the system for the most part evidently is "upgrading" existing trolleybus routes (with much of their alignment already considerably segregated) with little actual modification except for the guiderail slot installed in the middle of the pavement. Evidently, much of the existing power/OCS facilities were utilized – thus saving costs.
Since mostly existing routes were merely converted, large-scale purchase of right-of-way was apparently unnecessary. The longer, double-articulated BRT buses operate in streets pretty much as standard trolleybuses. The main items of construction seem to be upgrading of the OCS and some stations, and installation of the slot with the guide rail.
Apparently, Nancy transit managers didn't even think of reconstructing streets or relocating utilities – the common practice in both North America and Europe for most new LRT systems, even the installation of a simple "streetcar" (tramway). indeed, European LRT practice – and the prevalent trend in the USA – seems to be to combine LRT installation with a sort of urban renewal program. That has not only given anti-transit zealots like Wendell Cox grist for their mill, but is increasingly becoming an impediment to LRT development in many cities (with various "BRT" permutations being offered as the only lower-cost alternative).
In both North American and Europe, there seems to be a tendency to burden LRT with a variety of extra design elements and costs not deemed requisite for guided buses (or any form of BRT). in communities considering LRT vs. other possible alternatives like BRT, these design elements may need to be reevaluated, and reduced or eliminated, if LRT is to be assessed on a level playing field with such bus alternatives.
implications for LRT: KISS
In any case, Nancy's transit managers evidently abided strongly by the KISS principle (Keep it Simple, Stupid) and produced a reasonably priced project (if they could only get it to work properly). They apparently kept the focus on improving transportation, not implementing the Grand Vision of a World Class City. One might also suspect that the vendor (Bombardier) was closely involved, wanted a working showcase example, and insisted that planners cut the frills. Which raises the question: Why isn't this same practice followed with respect to LRT?
As previously noted, while the cost of Nancy's "guided bus" seems quite cheap compared with that of "standard" US interurban LRT (and European tramway) installations, it's important to realize that it's roughly comparable to the construction cost of comparatively simple LRT project, such as the Portland Streetcar (see photo at left), especially when the cost of electrification is backed out. in other words, Nancy have kept their sights on a "tram", no more, no less, and without the usual frills.
It's clear that LRT planners and contractors need to offer similar low-cost options and approaches. One possibility would be to offer a kind of "2-tier" LRT approach – either the "grand package" with urban makeover, or a more modest streetcar-style (or barebones interurban) system which just seeks to make a fundamental transportation improvement, reduce operating cost, and cut out the fat.
Will Nancy riders be fooled?
In any event, now that they've installed a "guided-bus" BRT, what have Nancy transit managers and city fathers gained for their money? Apparently, a faux-LRT system that sort of looks like a tram or light rail vehicle, costs close to the same, negotiates 13% grades, and can roll (very carefully) away from the guideway. The slightly improved operating speeds of the new system can probably be attributed mainly to improved signal prioritization, segregated lanes, etc. While a vehicle life of 30 years is claimed, in all probability the TVR buses have an actual life of 15-20 years (about half that of LRT cars), and resale value is questionable. Since Nancy has locked itself into a proprietary system, one can expect that rollingstock bids in future will be reflected accordingly.
As for the much-vaunted "tramway on tires", it is highly doubtful that the Nancy public will be fooled. it's rather likely that a TVR bus will pull up to the stop, and riders will think, "Ah, a nice new bus. What will they think of next?"
Certainly, one of the most important disadvantages of systems like TVR is the difficulty of bus vehicles to be entrained. That will almost surely mean that Nancy, with its "tramway on tires", will never see the operating cost savings which come from the ability to couple driverless vehicles into a trainset and improve operating productivity.
Yet, curiously, the subject of operating cost for guided bus systems is almost totally ignored in connection with "guided-bus" and other BRT operations, including Nancy's. By and large, the full cost of paveway construction and maintenance does not appear be allocated to the bus service in all cases, particularly when a portion of the route uses public streets – unlike the case with LRT, where strict accounting of costs is the norm. indeed, an LRT line may even be made responsible for elements of street infrastructure beneficial to motor vehicles.
Nevertheless, heavy buses – particularly giant vehicles such as the TVR buses for Nancy – exact inordinate wear-and-tear which is incurred as a social cost, one way or another. (it should be noted, however, that from the point of view of the transit agency, transferring costs to a separate public works department is a budgetary advantage, and this may tip the comparative evaluation against LRT in some cases.) "Guided-bus" systems could be expected to exhibit vehicular operating costs per hour significantly above those usually demonstrated by buses solely using public streets and highways (even reserved lanes and HOV lanes). if these costs are not given, they could probably be extrapolated or inferred with reasonable accuracy.
Systems using electric buses with OCS (like Nancy's) could be expected to exhibit operating costs per vehicle-hour quite close to those of LRT. in fact, one would expect maintenance costs of the guideway, and possibly vehicle maintenance costs, to exceed those of LRT. However, paveway installation costs may be reduced in some cases, either because existing pavement is used (with minimal alteration and no reinforcement), or because the original pavement had already been reinforced for heavy-duty bus service. Also, LRT often seems to be burdened with signallization costs not deemed necessary for bus service.
in view of LRT's typically larger vehicles and ability to operate in trains, in most cases LRT operating cost can be expected to be considerably lower than for "guided bus", at least where peak volumes utilize the greater capacity and eliminate the need for many extra peak tripper buses. in addition, it is doubtful that guided-bus systems, including those with the "pseudo-LRT" veneer, have fully equivalent appeal to the public sufficient to attract equivalent passenger volumes. Thus, one would expect cost per rider-trip and per passenger-mile in most cases to be significantly lower for LRT.
However, it is possible that some of the higher-level guided-bus systems (e.g., those with rail-like stations, electric propulsion, etc.) attract riders at a rate closer to that of LRT. But then, these systems also lack the ability of LRT to accommodate increased volumes at modest additional cost. in other words, for little to no capital cost savings compared with LRT, such "guided-bus" systems may, in all likelihood, burden operators with higher ongoing cost and less real-world people-moving capacity.
Does the "guided bus" fulfill a need?
So what have Nancy planners and decisionmakers now bought? They basically will have a system of elongated trolleybuses camouflaged as "trams", with lots of gadgetry to keep the buses on course. They will have a central slot to deal with in the middle of the paveway (tending to collect rain, mud, etc.). And they will be persistently trying to solve lots of operational challenges over the next months and years to prove the whole thing works. Thus one can safely predict that Nancy will be expending a lot of its planning and administrative energy trying to solve the challenges of making a trolleybus system mimic the performance of an LRT system.
There's a recurring question: Why bother at all with the guide rail in the slot? it is dubious whether such an arrangement will permit higher vehicle speeds, although Nancy designers seem to think their bus will run a bit faster in a narrow right-of-way if it's guided in this fashion. One is tempted to suspect that the extra-long, multi-articulated bus benefits from having its axles guided by such a mechanism, possibly minimizing any misalignment of the rear section while in the guideway (which might explain why the vehicle tends to "fishtail" when free-running).
And beyond the question of whether it's worthwhile trying to imbue a bus with LRT characteristics, there's another issue as well. Once a transit agency or government entity buys into an entire, specific "guided-bus" technology, its planners and decisionmakers commit to a specialized guideway and technical infrastructure using one form or another of specially designed curbs, below-pavement conduits, special travel lane markings, etc. That might happen after the initial order of vehicles, where competition is alive and well, and the initial bidding environment may be fairly competitive among a number of vendors.
However, the agency then has a stock of specialized buses with a 12 or 15-year life expectancy and capital costs sunk into building a specialized guideway which may work properly with only one manufacturer's product. When the agency proceeds to expand the fleet or must find replacement buses, it may well find itself "trapped" with only one manufacturer/bidder. is any vendor going to assure transit planners that its proprietary technology will become an industry standard in the next dozen years? it's not much different from going with a monorail, Maglev, or some other basically proprietary technology.
in contrast, imagine instead that the transit agency set down a few miles of steel rails with 1435 mm (standard) track gauge with readily available, dependable track switches, and mature signalling technology. The agency buys a couple of dozen light rail vehicles which have a lifespan of 30 to 50 years with trainlined controls so that one operator can control two to four cars. When it's necessary to expand that system or replace the vehicles, the agency will find at least half a dozen suppliers lined up who can make cars which will work fine with the previous generation. Productivity is better, competition is alive and well, and the technology is mature.
Again, one might well ask: Upon which aspect of rail transit does a "guided bus" offer improvement?
For information used in this report, Light Rail Progress particularly wishes to express appreciation to the following: Mike Taplin, Light Rail Transit Association, for his draft of a forthcoming report; R. Eacker, PE; contributors to the Light Rail Progress Professional online discussion list; Lightrail.com website, for Portland Streetcar (Skoda streetcar) graphics; Greater Nancy Urban Community website for data and graphics of Nancy BRT.Rev. 2001/03/29