and operational trial
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by Tony Wilding, MIMechE, MIRTE AT the beginning of September last year. Perkins introduced its turbocharged 6.354 diesel. And one week later came the Dennis Defiant 24-ton-gross tractive unit, the first chassis to fit this new engine. On a recent full road test and 732-mile operational trial both chassis and engine gave a good account of themselves.
With a torque of 378 lb ft, only 20 lb ft lower than the Perkins V8, the T6.3$43 gave the Defiant a performance comparable to that of 24and 26-ton-gross chassis tested with the 179 bhp vec. Although having 13 per cent less power (155 bhp), the Defiant gave similar through-gears acceleration times as the VS-powered 24and 26-ton-gross chassis. And similar average speeds were returned over comparable sections of the operational trial.
For the first time, use was made of M6 extension which takes this motorway beyond Penrith and which, since the end of October, has allowed the difficult 36 miles through Kendal and over Shap to be avoided. This improvement in the route to Scotland cut at least one hour off the
normal time for the run and enabled the 376-mile first leg of the operational trial to be completed in just one minute over 9hr—at an average of 42.0 mph.
Ice on roads
Average speeds on the run south were kept down by very bad weather. There was ice on the roads at the start and a lot of snow in Scotland and the North East and rain elsewhere hut even so the average was a commendable 35.9 mph and the overall figure for the 732 miles was 38.8 mph. Overall fuel, consumption turned out to be 7.9 mpg, the same as with the 26-ton-gross vehicle having a Perkins V8 but tested in the summer of 1969 in far better conditions—temperatures this time were around Odeg C for the whole run—and 0.2 mpg better than the 24-ton outfit with the same vee engine tested at the beginning of 1970.
When the Defiant was introduced, one of the design aims was stated as being obtaining a robust vehicle with low unladen
weight. It was expected that payloads of about 17 tons would be possible on a single-axle semi-trailer within the 24-ton limit and this was not far off the mark as we carried 16 tons 17.25cwt.
The Defiant is 'lighter than its rivals in the 24-ton-gross tractive unit field and much of this is due to the use of the turbocharged engine. It is worth noting here that this power unit is not simply a turbocharged version of the 6.354 but that it is a completely redesigned engine to accept turbocharging to ensure at least a comparable life with the naturally-aspirated 6.354 in spite of the higher stresses involved.
Except for the engine and use of a higher-capacity -version of the Dennis gearbox, the Defiant is based largely on the manufacturer's 15.5-ton-gross four-wheeler. The front axle, the Eaton two-speed axle and the brakes are the same except that lock actuators are fitted to the front brakes as well as the rear and diaphragm size has been increased all round.
The chassis has a heavy-duty Borg and Reck clutch to cope with the increased torque and changes to the gearbox include wider teeth which has necessitated the addition of an extension casing at the rear to contain the first gear train; there is now constant mesh engagement on all ratios.
The frame is stronger on the Defiant with thicker top and bottom flitch plates and suspension changes include softer front springs but stiffer and shorter rear springs. With the location of air-intake cleaners behind the cab the hump in the bonnet in the 15.5-ton chassis is eliminated and it is
First tests carried out with the Dennis were set-route fuel consumption , cheeks followed by timed acceleration runs and brake tests. With 8.8 mpg over our usual 6-mile out-and-return run on A6 near Luton and 8.2 mpg on a full-throttle motorway run the pattern which was to be followed in the subsequent operational trial was set.
have already referred to acceleration times as being equal to those of similar Weight chassis with the 'higher-power Perkins V8 and extremely good braking figures were also obtained showing worth while improvements over almost all similar-weight art ics previously tested by CM. The high standard figures were obtained even though the road was slightly damp at the time of the test and except for persistent locking of the driving axle offside
wheels there were no heavy marks left on the road surface. The reason for this locking came to light during the second day of the operational trial after the brakes had been used a good deal on the hilly A68.
Heavy smoke pouring from the offside rear brake of the Defiant showed that too tight adjustment was causing this unit to do more than its fair share of the work; a stop had to be made to "back off" the brake shoes.
Apart from the 10-minute hold up to attend to the brakes the operational trial went well. The Defiant was cruised at or close to its maximum speed of 61 mph where possible on the motorways. speed reaching up up to 67 mph or so on occasions when on overrun. And there was adequate power to cope with the hilliest stretches of the route--on the run across the Tweedsmuir hills in Scotland and down A68. The satisfactory level of performance is indicated by the good averages of 27.2 mph on the easier first stretch of A68 and 21.4 mph on the more difficult part after West Woodburn.
The new section of M6 has a good climb from the A65 junction for the eight miles to the Kendal turn off. Here the Defiant did well to average 36.9 mph and for the next 14 miles where there is still a general up gradient, the average was 46.7 mph.
The climbs of the three most severe hills on the route were timed. The 1.82-mile-long Carter Bar on the Border was climbed in a total time of 7min 44sec. The speed at the bottom was 39 mph and for almost the whole climb second/high gave just the right ratio for the ascent with road speed varying between 14 and 18 mph on the 1 in 13/14 gradient. Near the top where the slope increases to 1 in 9, second /low was needed and the speed dropped to 10 mph before reaching 16 mph at the summit.
On Riding Mill where there is a sharp right turn at the bottom the climb was started at 9 mph in second/high. On the steepest-1 in 5—gradient first/low was needed and road speed fell to 2 mph. At the top upward changes had been made as far as second/high, road speed was 12 mph and the 0.6-mile climb had taken 3min. 49sec. Castleside Hill is also severe, having a gradient of 1 in 5.25 not far from the start. At the bottom, speed was 32 mph and on the steepest section first /high proved adequate with the road speed dropping to 4 mph. After the 0.8-mile climb which took 5min 9sec the speed was 19 mph in third/ low.
The ratio steps provided with the Dennis five-speed gearbox and the two-speed axle are not at all even, as is illustrated by the maximum speeds in the gears quoted in the table. This meant that there were few occasions when real advantage could be taken of "split changes". For example, there was only 3 mph difference between the maximum attainable in second/high and third /low and between fifth/low and fourth/high. But there were occasions where the two-speed axle did allow just the right ratio to be obtained. The Carter Bar climb was one of these and so was the long climb at Moffat on A701. This' uneven spacing also resulted in a long time being needed to learn how to make perfect changes in the box.
The only major criticism that I.have of the Defiant is that the noise level in the cab was rather high and the front suspension too hard. I would say that the engine noise was slightly less than in the case of the Dennis 15.5-ton model with 6.354 but there is room for further improvement. Initially, the suspension did not seem too bad but after a couple of hundred miles in the cab a reduction in the bumpiness would have been appreciated. The springs were well damped and it may have been that the dampers were responsible in some way for the harshness.
Steering was reasonably good but concentration was needed to steer a chosen line and care had to be taken when making slight changes in direction. There was a feeling of "rubberiness" with a short lag between movement of the wheel and the vehicle changing direction and then the power assistance seemed to catch up and give an oversteer characteristic. This was not a serious problem and one that reduced with experience of the vehicle.
A feature of the Dennis cab is the excellent forward visibility and the high proportion of screen cleared by the wipers. Access to the cab is easy, especially now that there are grab handles on the dash at both sides. There is a spacious interior and the standard of finish is high. Dennis fits heaters with the generous capacity of 7kw. These kept the interior comfortable in spite of the low temperature outside. But the heat output was only just adequate except when the engine was working hard. The engine seemed to run relatively cold and there may have been benefit with a temperaturecontrol fan or radiator shutter.
As tested, the Defiant has a basic list price of £3975. With 55ga1 fuel tank which is now standard; the price is £3820 and if 24V electrics are required there is an addition of E60. ON a recent visit to North America I was able to spend some time studying the development of bus transit in the States.
This left me with three main impressions: First, the major new emphasis, announced by the Department of Transportation, on moving people —rather than vehicles—on urban freeways.
Secondly, the enormous potential capacity of freeway systems to move people if adequate bus priority measures are imposed.
Thirdly, the ability of the bus, if used in rather more sophisticated ways than we . are accustomed to in this country, to provide an attractive alternative to the private car for some purposes.
My overall impression was that the United States are far ahead of Britain in developing the use of the bus for mass transit, particularly for the longer distance journey to work.
The reasons for this are historip. European cities were already old during the Railway Age. To expand they built radial railway systems to bring workers into the city centres. Having established such systems, the natural tendency was to extend them as the cities expanded rather than to consider alternatives. The streets of the old cities were narrow and congested, and the bus gained the image of a slow-moving vehicle hampered by other traffic.
In America mass car ownership came sooner, and there was space and money to provide wide roads. Buses, therefore, did not have to operate under such difficult conditions as in Europe. The main factor, however, was probably the spanning of major barriers by roads before there were rail routes: in Britain the Forth was spanned by a rail bridge for more than 70 years before a road bridge was built.
San Francisco's water barriers were first spanned by road, although one of the bridges initially had a tramway. As a.result, road-based public transport developed to carry commuters across these barriers. Manhattan is linked to the east by several rail systems, and rail comMuting from this side is the normal practice. From the west access to mid-town Manhattan is by the Lincoln road tunnel and here again bus transit has developed extensively.
Buses are carrying heavy passenger loadings over distances which in Europe would be regarded as the exclusive province of rail. In the States the two systems have been treated as alternative modes, and detailed comparative studies have been made. Hardly any work on these lines has been done in Europe.
The classic study is of course that by the Rand Corporation—"The Urban Trans portation Problem". This demonstrated the tremendous advantage of the Freeway-flier bus, both in cost and convenience. More recent work has shown that it greatly underestimated the capacity of freeways to carry buses, and correspondingly underestimated the cost advantage of bus transit.
My first visit was to the Department of Transportation in Washington DC, where I found agreement on the impracticability of trying to build freeway capacity in cities to carry the full peak demand for the journey to work by car, and the undesirable effects of trying to do so.
In general the States now have freeway systems adequate for off-peak traffic, and the efforts of the Department are directed at determining how much additional capacity should be added to such systems to handle peak-hour demand, and in what form it should be added. It considers such alternatives as additional lanes for tidal flow, or for use by car pools or buses only The result has been a major change in policy emphasis from moving vehicles to moving people. There is strong support for measures for assisting bus transit as the most economical solution.
At the department I met Don Morin, chief of the public transportation branch, urban planning division. He is a real enthusiast for bus transit, with a strong belief in its ability, given reasonable operating conditions, to attract people away from their cars. He lives at Reston, Virginia, a high-income suburb 20 miles from Washington. No bus company would consider providing a service, so the community association chartered a bus. Two years later they have 11 buses on charter and a waiting list—and this in the land where it is supposed to be almost impossible to separate people from their cars.
Cost to the individual is greater than for a car pool and about the same as the commercial parking in downtown Washington. Many people using car pools are
becoming disillusioned because of their unreliability, variability, and sometimes because of incompatibility and the• necessary organizing.
A recent experiment in Peoria, Illinois, with a similar specialized bus service proved successful in attracting car owners, who accounted for 72 per cent of the travellers on the new service. This service accepted zig-zag routeing at the picking-up end in order to collect passengers close to their front doors, and gave a high level of reliability and convenience.
The Peoria service was also a financial success. A friendly club coach atmosphere was established as riders in each bus got to know each other. There were obvious objections to buying a monthly season which was only valid for one bus each way each day; the advantages outweighed these, and passengers would use their own cars if they occasionally had to work late.
The bus has an immense advantage over tracked systems in being able to provide a near approach to door-to-door transport without a change of vehicle. The car owner usually demands this level of convenience before he can be persuaded from his car, The San Francisco Oakland Bay Bridge bus operation is an interesting one. One lane carries up to 12,000 passengers an hour in 340 buses, but it is not an exclusive bus lane; about 1250 cars use it in the same hour, which means that the buses are using rather less than one third of its passenger capacity if all vehicles were buses. Its capacity must, therefore, be at least 36,000 passengers an hour, although the lane is only Ilft wide, has no hard shoulder and very limited lateral clearance.
One • might compare this with London commuter rail lines; at only three main line terminals do hourly loadings per rail track exceed 12,000 passengers. Don Morin gives the capacity of a full motorway lane as 50,000 passengers an hour. General Motors trials have shown that buses in a single lane can carry up to 60,000 seated passengers an hour at 55 mph, using average drivers and no special controls.
Bypass for buses A recent study of the above system by the California Department of Public Works decided against enforcing an exclusive bus lane, because of delays to cars and waste of capacity in the lane. It seems illogical to worry about the cars when buses using a third of one lane out of five are carrying almost half the passengers crossing the bridge. However, the Department did suggest a bus bypass through the toll plaza. This has now been put into effect—the buses no longer have to stop to pay tolls, and have a 10-15 minute advantage over the cars, • It would be interesting to see what switch took place to buses as a result of this measure, but by 1972 San Francisco Bay Area Rapid Transit railway will be operating. A problem mentioned by Don Morin is that there are never enough buses to fill a bus-only lane, and there is always unused capacity. The Department is therefor considering permitting the use of the bus lanes by car-pools with a minimum number of passengers per car. A trial scheme is proposed in Cleveland.
Among other bus projects discussed at the Department, but which I did not visit, was that for exclusive bus lanes in the median of the Shirley Highway which links Washington with rapidly expanding suburban areas of Northern Virginia. At present only four miles are open, but this gives buses a 12-18 minutes time advantage, and has increased passengers by 30 per cent. The next seven miles of the bus lane. taking it as far as the Potomac River, are now under construction in advance of the main highway. This is expected to give the buses a half-hour advantage and double the number of buses using it to a total of 200.
Although the extra 100 buses represent two lanes of freeway for people in cars, at average occupancy, the buses will still only be using a small proportion of the capacity of their exclusive lanes. It has been suggested that 200 buses per hour is the minimum that could justify exclusive use of a freeway line (Highway Research Record No. 59).
Another project is on a six-mile length of Interstate 5 in Seattle. At one end is a large car park while at the opposite end exclusive on and off ramps take buses into the heart of the downtown area. In conjunction with .a contra-flow bus lane on the city streets, this almost halves the peak-running time for the buses. Cars are carried past the downtown area and have to make their way back on crowded city streets.
After Washington my next visit was to New York, the home of the famous Port Authority Bus Terminal (CM December 25 1970). This has developed opposite the eastern end of the Lincoln Tunnel because, as mentioned earlier, the latter forms the main route for commuters from the New Jersey side. Ramps lead directly from the tunnel mouth to the two short-haul bus decks.
When discussing •bus transit in this country people sometimes wonder how heavy passenger flows at the end of a bus route could be handled. The New York Terminal is a concrete answer. Occupying one block, 800ft by 200ft, it is used by more than 40,000 passengers in a peak hour. Proportional to area this is about the same intensity of use as at Charing Cross station, and substantially greater than at Waterloo main line station.
I spent the evening peak-hour moving about the bus decks. A continuous stream of passengers came up from the concourse and were cleared as fast as they arrived by the steady flow of buses up and down the ramps. Half of the next block to the north has been cleared, and work on an extension to the Terminal will start shortly.
At present it is used by 39 bus companies. If, on average, each company ran three routes—an underestimate—this would involve over 100 different services. This indicates the flexibility of the bus as a vehicle to take people close to their homes.
Buses have always had an advantage in the evening, with their direct access to the tunnel, but inward-bound in the morning they were subject to the same delays as cars, although 85 per cent of the passenger flow was carried in only 15 per cent of the vehicles. To remedy this, and to make better use of the tunnel, which has tidal flow through the centre bore, a contra-flow bus lane has recently been introduced along the full length of Interstate 459 which links the New Jersey Turnpike with the tunnel. Part of this link, the Union City Underpass, was built in the 1930s and has three 10ft lanes each way with no hard shoulder.
Gantry signs indicate that the bus lane is closed to westbound traffic, and rubber posts inserted each morning mark it off from the westbound lanes. If the scheme is made permanent, posts which can be automatically retracted will be installed. This very sub-standard lane carries about 22,000 passengers in 500 buses during the morning peak hour.
The buses save an average of 15 minutes. on less than two miles of road. The capacity of the road is better matched to that of the tunnel, since each link has four lanes eastbound in the morning. The project is being managed by the Port of New York Authority.
There is a park-ride facility at the Bergen Viaduct, near the western end of the link. The cost of an inclusive parking /bus ticket is about half the cost of parking at the Bus Terminal. This idea has proved very successful, but the Authority considers that any future parks should be sited further out of the city to limit congestion at the western interchange.
The long-distance coach companies, Greyhound and Continental Trailways, have their station in the basement of the Terminal. Returning from New York, the 180 miles from the Terminal to the Baltimore City boundary took me three hours—an average speed of 60 mph—the only stops being to pay tolls. The journey was comfortable, with no impression of haste.
Milwaukee revival My last visit was to Milwaukee, on Lake Michigan, an attractive city of over one million people. The business district had started to decline due to serious congestion, but construction of Interstate 94 and other freeways passing close to it has reversed the trend. The city does not appear to have a traffic problem at the moment. Traffic • on secondary routes is beginning to increase again as the freeways fill up, however, but the authorities have bought enough time to plan and build a transit system.
Most bus priority projects might be considered as improvisations to make better use of existing streets and freeways. Milwaukee is of interest since it is one of the first attempts to plan an integrated transit system for a major city which will use only buses.
Milwaukee pioneered the "Freeway-flier" bus, running direct between out-of-town shopping centres, which provided free parking, and the business district. The present project grew from this, and will provide a 7+-mile transit link in an east-west direction, fed from the west and from. the north-south freeways, and delivering traffid to the business district at its eastern end. Along this link lie other major traffic generators.
The project was not tied to bus operation from the start; various systems were evaluated, including monoand duo-rail, Skybus and StaRRbus, for the main link. The report came out in favour of the Advanced Design Bus, a GMC gasturbine-powered project. This was more expensive than a system using standard buses, and the units might be considered to have an unnecessarily high performance for the task, but emission of pollutants from the exhaust is less than one-tenth of that from a standard diesel bus during acceleration.
Flexibility of buses Speeds of 70 mph were specified as desirable for the bus, though not for rail, in order to be faster than maximum car speeds. This seems unnecessary in view of likely car speeds in peak hours and the small difference in journey times at '70 and 50 mph over the length of the transit link. Owing to the high speed selected for the bus, a very lavish formation width was specified for the line-haul portion of the bus route. In spite of this the bus won comfortably on total systems costs, as the downtown distribution system could be on the surface.
To quote from the evaluation report: "Specifically, a major factor in the decision to select the Advanced Design Bus was the flexibility that rubber-tyred transit possesses. The vehicle can operate both in mixed traffic and on exclusive rights-of-way, and thus can be used for collection, line-haul and distribution functions.
"This service capability maximizes the potential for a one-seat ride. The system can readily be adapted to a demand-bus service to improve collection of passengers in outlying suburban areas. The level of service or area of coverage can be improved or expanded by adding more vehicles to the system."
The elimination of time wasted in interchange is of the utmost importance in attracting people away from private cars. Such passenger time costs are seldom taken into account when evaluating rival systems. The bus road will have capacity up to three times the forecast passenger demand for the year 1990 without a significant loss of operating speed. Two routes for the transit link arc now being evaluated in detail, and construction should begin in the early 1970s, The careful evaluation of all transit systems made in the Milwaukee study is a welcome change from the Manchester Rapid Transit Study which rejected serious study of bus transit on the flimsiest grounds, largely because, being so different from conventional tracked systems, comparison was difficult.