Picture taken from the Huffington Post and also found on numerous web sites.

Q: What is it?

A: It's like a "bus on stilts", that lets traffic pass under it while it makes stops for passengers to get on and off. Bus stops, or stations, are at second floor level to meet the doors of the straddling bus or in some cases at third floor level (transfer to another bus line on an overpass) with a trap door on the bus roof, and stairs going down.

Q: How big is the bus?

A: Preliminary descriptions suggest that the bus would be about 20 feet wide, 14 to 20 feet high, and up to 200 feet long with flexible segments for the longer models so they can go around curves. Different dimensions, particularly the height, could be had for different situations. Passenger capacity up to 1400 has been suggested.

Q: How many lanes does the bus occupy, or straddle?

A: The models proposed occupy two lanes. With some designs, there is space underneath for cars to travel two abreast.

Q: How fast does the bus travel?

A: The designers anticipate a maximum speed of just under 40 miles per hour (60 km/hr.). Speed will be much less in a typical urban environment.

Q: Don't bridges and underpasses have to be rebuilt for the bus to fit underneath?

A: Usually not. A few different versions of the bus are proposed. One model will fit under most existing highway bridges. It is no higher than a tractor trailer truck (about 14 feet high) and only allows regular automobiles (less than 6 feet high) to pass underneath. Other proposed models would let larger vehicles, even tractor trailers, pass underneath but could only run where there are no underpasses or where the road was specially built with higher underpass clearance. Incidentally some of the difficult overhead structures to work around are the trolley wires that some other buses use. The undercarriage does not telescope up and down; the bus body remains at the same height at all times.

Q: Won't the bus prevent motorists from making turns?

A: No. Cars usually won't be under the bus for long periods of time. The car driver under the bus would let the bus move on and the side street or exit ramp he wanted to turn into will then be open.

Q: What keeps motorists from driving in and out among the stilts under the bus and getting hit by the stilts if the bus starts moving?

A: The side carriage of the bus is a continuous wall or rail as opposed to being individual stilts. There would be front to back accordion-like or telescoping portions to let the entire bus body bend around curves without leaving gaps that someone might drive or walk through..

Q: How does the straddling bus turn corners?

A: For most of its normal route, the bus only makes gentle curves. Drivers of other vehicles can follow the roadway underneath no differently than when driving in a tunnel. All the driver sees are lane lines and perhaps some warning lights if he gets too close to the side (the bus' wheels and frame). Should the bus have to make a sharp turn, it would stop first. The rear would be closed off and a flagman, or the driver with the aid of video equipment, would ensure nobody was under the bus before it turned. Sharp turns would only be made where the roadway was designed with enough maneuvering room for the bus. A separate traffic signal phase would be provided for the bus to make a turn at an intersection.

Q: Is it possible for cars to be under the bus and make a sharp turn with the bus?

A: It could be done but this appears to be a feature that costs more than it is worth. Better would be a separate traffic signal phase for the bus. If both cars and the bus were waiting at a red light, the bus gets a green turn arrow while the cars have a red light. For cars to make a sharp turn with the bus there would have to be solid lane lines visible beyond the front of the bus. They could be permanent lines whereby all buses and all cars make the same turn, or lines made from daylight visible flashing panels in the roadway that indicate which way the bus is going to move..

Q: Won't the bus mow down cars and bicycles in front?

A: This is the responsibility of the bus driver. In a simple operation, the bus waits behind vehicles in front rather than driving over them, although cars will overtake the bus from underneath. There should be sensors that will stop the bus if it is about to hit something up ahead.

Q: Can the bus overtake traffic?

A: Yes under some conditions. The driver must be sure that the side carriages of the bus will clear any turning or lane changing cars up ahead and also be sure he is not going to overrun a vehicle that is too tall. The opportunities to overtake will likely be very few. Ahead of the bus, cars will likely be too close to the sides of the lanes for the bus side carriages to clear.

Q: Can the straddling bus improve bus transit even if it gets stuck in traffic jams?

A: Yes.

* One large bus with several doors for loading at a large station operates faster than many regular buses that have to wait their turns to pull into a bus stop.

* The bus does not have to wait to merge back into the flow of traffic at each stop.

* Each straddling bus "removes" perhaps two dozen ordinary buses from the roads.

Q: Can the bus use ordinary tires and operate on ordinary roads?

A: Yes provided that there are no sharp curves and there is enough overhead clearance and also enough pavement width. Ideally there needs to be a guard band of pavement (like a bicycle lane) on both sides of the bus lanes for the wheels and side carriages of the bus to occupy. For some models, tracks similar to streetcar tracks will be laid in the road. If there are no rails and no sensors to keep the bus centered over its lanes, there will aways be fewer lanes under the bus than the width of the bus occupies for example one lane of traffic under a bus that is two lanes wide, since motorists will stay further away from the side carriages of the bus.

Q: With the bus speeding up and slowing down, won't drivers find it hard to keep track of their own speeds?

A: Regularly spaced markings (in addition to lane lines) can be painted on the road. Arrays of small lights producing an animated pattern can be added to the bus side carriages to simulate stationary objects for drivers underneath to judge their own speeds with.

Q: Doesn't the road have to be wider than it might otherwise be in order to accommodate the straddling buses?

A: In most cases, yes. Otherwise the side carriages either take up part of the lanes under the bus or take up part of the next lane to the side. This will produce a choke point for vehicles, but this may be acceptable, either having vehicles under the bus get into single file or having overheight vehicles or additional traffic passing to the side of the bus get into single file. If there is already a bike lane that the bus side carriage might occupy, the additional roadway width to avoid choke points would be minimal. In all cases the roadway will not have to be as wide as a roadway with an extra lane exclusively for buses.

Q: What happens at a fork in the road?

A: Projected light beams can be added to make lane markings on the pavement for cars to follow. Motorists under the bus must follow lane markings including any projected on the road by the bus. If buses can choose a fork branch then the best lane markings in a fork would be illuminated panels embedded in the roadway that match the bus route. Also a motorist can slow down and allow the bus to pass on when approaching a fork in the road. Lane lines, both painted and illuminated, must be continuous to inhibit cars from immediately veering to the side after exiting the front of the bus.

Q: What happens at an intersection?

A: The bus may have traffic lights underneath it that mimic an upcoming traffic signal so cars don't shoot out from under it into an intersection against a red light. The sides of the bus are continuous at ground level. If the bus happens to stop in the middle of an intersection, cars on the cross street are blocked and cars under the bus remain in place or continue on. Generally the bus won't stop before an intersection except for a red light in which case there should be separate signal phases for the bus and for turning cars.

Q: What happens where two roadways merge?

A: Traffic signals are pretty much mandatory. This is to prevent problems where cars alongside, including those on the main road,have to stop abruptly to get behind what may be a very long bus. Also there are merge conflicts with cars coming out from the front of the bus as well as with the bus itself, which only traffic signals can control.

Q: What if the bus needs to change lanes?

A: This should not happen except at designated locations where there are markings on the road and traffic signals to control all movements, or where there is someone directing traffic. In normal operation the bus remains behind overheight vehicles and other traffic it cannot overtake while in its own lanes.

Q: How do drivers know where their desired turnoff is given that "traffic signals" under the bus are moving with the bus and visibility to the side is restricted?

A. No harm is done if the car driver stops a little too soon and when the bus moves on, the car driver continues up to the intersection which is now in full view.

Q: Is it mandatory that drivers go under the bus?

A: No, particularly if drivers want to make a turn or choose which side of a fork to take, or if the car is too tall. Drivers in China are accustomed to waiting for a vehicle alongside to pass on before changing lanes, sometimes being "in the wrong lane" and holding it up much to the chagrin of others.

Q: How does the bus turn around at the end of the line.

A: The bus may have controls at both ends so it doesn't need to turn around. Still, it is necessary to stop traffic for a minute or two while the bus turns off into a parking area or shifts over to the other side of the street.

Q: Will the bus operate contraflow or over both lanes of two way traffic?

A: No. The bus may only operate in the same direction as traffic that may pass under it. There is too much of a chance of collision with opposing traffic in the event of human error or mechanical malfunction particularly when overheight vehicles are involved.

Q: How is the bus steered?

A: Each wheel needs to be steered individually using computer control, or run on a track. Electronic sensors are used to keep the bus on a specific course and route. Such sensors could follow a painted line. While there may be manual override using a steering wheel, the computer control is still needed to keep the rear of the bus following the same path as the front and not jumping curbs.

Q: How do we prevent minor swerving by the bus from causing vehicles underneath to sideswipe?

A: If roadway and/or lane width is critical, the bus should run on a track. If the bus does not run on a track, the lanes underneath it should be wider than normal. This may mean having just one lane underneath a bus that occupies two lanes. Usually, driver behavior under a free steering bus will result in having just one lane of traffic underneath. The bus should have sensors to stop it if it veers too far off course.

Q: What difficulties might be encountered with tracks?

* The side carriages of the bus might not hold each pair of wheels exactly the same distance apart given that there are no full length axles and the side carriages may be slightly deformed from wear and tear, or from collisions with other vehicles. This can be solved by using unflanged wheels on one side of the bus and more elaborate flanges on the wheels on the other side.

* Given that any railroad track guides a train by forcing the train to follow it, the straddling bus track must be strong enough to guide the large bus and also be smooth enough for other vehicles to drive over at intersections and when changing lanes.

* When tracks are installed without first laying ties and then reconstructing the roadway, the distance between the rails may vary slightly. This may be solved by using unflanged wheels  (or rubber tires) on one side of the bus but that requires that the rail on the other side be more robust to guide the bus.

Q: What difficulties might be encountered using rubber tires instead of steel wheels and tracks?


* The rolling resistance is greater with tires on pavement so the bus would consume more energy.

* The side carriages of the bus would be wider, so a wider guard band is needed between lanes where the side carriages run.

* Even with the best of steering, the bus will still swerve slightly, and the lanes underneath it would have to be wider.

Q: How does a driver wishing to turn avoid having a bus come up from behind and interfere with the turn?

A: By driving onto the guard band (if any) or obviously blocking the part of the lane the bus side carriage uses. If the side carrage of the bus is on the other side of a roadway guard rail, it will be necessary for the car driver to either stop prior to the turn or be well into the turn long before a bus approaches from behind. Traffic signals will regulate the movement of the buses and turning vehicles.

Q: How are too-tall vehicles kept from getting stuck under the bus?

A: While this cannot be prevented entirely, there are a number of techniques. Sensors and flashing lights would warn the truck driver as he approaches. A fringe of chains could be mounted on a frame and hung several feet behind the bus to make noise against a truck's roof if the truck gets too close. A cloth curtain can be provided to be lowered and block the driver's view. A stout horizontal lintel or girder would protect the back of the passenger compartment if another vehicle does rear-end the bus. For one model, overheight vehicles are prohibited from the bus lanes and stationary arches or lintels are mounted over the roadway at intervals. The bus passes over these and private vehicles must fit under them.

Q: What problems would be caused by having stationary arches over the roadway to keep overheight vehicles out of the lanes?

* Arches that provide enough clearance for vehicles to pass under would require that the bus be a little wider and a little taller than it might otherwised need to be, in order that the bus can pass over the arches, given that the arches take some horizontal and vertical space.

* The arches, if unusually narrow, might produce choke points in a two lane roadway because vehicles would crowd the center line.

* If an arch became deformed by an overheight vehicle, it could block the buses.

Q: What would keep the passenger compartment from falling to the ground in the event of a collision?

A: Supposedly the undercarriage and side carriage would be designed so that most of it together with the offending vehicle would still support the passenger compartment.

Q: What would keep the bus from tipping over in the wind or in the event of a collision?

A: Most likely the bus, given its width, would not tip over.

Q: Won't motorists feel claustrophobic?

A: "Windows" in the bus undercarriage would make the view from underneath less confining. If one felt uncomfortable driving too close to the undercarriage of the bus or the side of a tunnel , he would drive closer to the center and traffic under the bus would be single file at that point. Or he may remain behind the bus. At least the entire width of the original lanes should be open under the bus.

Q: What if I am changing lanes and the bus is coming up from behind me?

A: In most cases the bus won't be overtaking cars that fast, probably no more than 10-15 MPH faster than you are going. So it can stop quite quickly. At any rate you will see in your rear view mirrors the side carriages of the bus coming up, not unlike a pair of motorcycles. It is your responsibility to make your move with enough advance warning; if the bus strikes your side, you would probably be at fault.

Q: Won't the bus be a hazard if drivers are not attentive around it?

A: It would be no more hazardous than driving alongside an ordinary bus or a large truck, or driving in a tunnel.

Q: How does the bus operate amidst overheight vehicles on a roadway that it straddles the entire (2 lane) width of?

A: The bus and the overheight vehicles remain in line and hopefully one of the lanes will be kept free for smaller vehicles to pass through the bus and overtake.

Q: How is the bus powered?

A: Electrically. A combination of supercapacitors, charging stations, and perhaps solar panels will be used. At bus stops and/or at intervals along the route, electrical contacts on overhead brackets brush over strips on the bus roof to transfer power to the bus. Capacitors store electricity for the bus to make it to the next charging station. As the largest current draw occurs when starting up, charging stations at bus stops and/or stoplights can allow the bus to accelerate while still collecting power from the charging station, saving more stored power for travel between charging stations. Most likely the straddling bus will not be powered using a continuous overhead trolley wire system.

Q: What is a supercapacitor:

A: A capacitor stores electricity as "packed electrons", more correctly, as an electrical charge. This is vaguely equivalent to a balloon's storing compressed air that can do things such as let the balloon rocket about if let go with the mouth not tied shut. A supercapacitor stores enough electricity to be "let out a little at a time" which amount is enough to power the motors, and the charge lasts long enough to run the bus perhaps a half mile or more. Contrast that with a battery which uses chemical action to produce electricity. There are some electric buses operating in Shanghai and a few other cities that use supercapacitors instead of trolley wires or batteries.

Q: Would exhaust fumes from cars under the bus accumulate and be drawn into cars?

A. There would be vents or "windows" in the bus side carriage to let fumes dissipate. But the side openings would not be large enough for people to walk through or cars to drive through.

Q: Is a two lane 20 plus foot wide body required?

A: Together with the undercarriage, the bus would have to be nearly two lanes wide in order to have one easily navigated lane under it.

Q: What is the most likely collision under the bus.

A: Two drivers traveling alongside each other sideswipe each other while trying to stay clear of the bus side carriages..

Q: Could the buses be made to straddle three or more lanes?

A: This would require a more robust frame for the bus that would require more vertical space between "tunnel" ceiling and passenger compartment floor and thus a higher bus overall. Also it would require a higher passenger load along its route to justify having such a large bus.

Q: Wouldn't the bus have more problems in cities where there is a high collision rate among existing drivers?

A: We believe that the bus, owing to its size, will encounter few problems.

(Q:) It will never work.

A: They can build one straddling bus line first and give it a try. According to the news reports, China has construction plans for about a hundred miles worth of this bus technology planned for 2010 through 2011 with the first lines to run in Beijing.

Last updated 9/1/10

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