Bridges were the first elevated roads, allowing the landscape to flow uninterrupted beneath them. This was good for the flow of traffic and also for any rivers that might have been flowing through anyway. It’s usually easier to build a bridge than to build a dam, divert a river, or scrape away at the sides of valleys.
This is Shanghai’s Yan’an East Road Interchange. This part of the Yan’an Elevated runs through a belt of publicly accessible green space created by requisitioning and demolishing buildings. It’s a useful way of compensating for the presence of elevated roads.
Doing something similar wasn’t an option for the central Chinese city of Chongqing hemmed in by four different mountain ranges between which flow the Jialingjiang River and the Yangtze River that’s still navigable by vessels up to 5,000 DWT despite Chongqing being 2,700 kilometers inland. With valleys running north-south and the Yangtze flowing west-east, Chongqing has always been a crossroads but, in mountainous regions, level land is too precious to waste on interchanges. On a mountainside just outside the city is Huangjuewan Overpass, also called Panlong Interchange, with twenty ramps, five levels and roads leading in eight directions. Some of the land beneath it is cultivated.
It’s preferable to building elevated roads over rivers as happens in Tokyo.
Elevating roads means the ground surface can still be used for things it was meant to be used for. These next two images of Hong Kong have pedestrians, shops, trees and low-speed local traffic at ground level.
This is all very well when as the traffic on the elevated road all thru-traffic with no need for traffic lights. Changes of direction can be still accommodated without the need for land-hungry slip roads and underpasses.
The most obvious place to put elevated roads is above existing roads but, even then, the space between the supports and the supports themselves can still be greened. The space below doesn’t have to be pedestrianized to be have amenity value.
This space can be used in all manner of ways as long as the roads remain elevated. Even the spaces circled by cloverleaf access ramps can be used or enjoyed if there’s a way to get to them.
But whether the ramps are straight or circular, this becomes impossible where the roads connect the high-speed traffic system with the low-speed local traffic system.
The problem is compounded at surface interchanges with many ramps. It’s possible, though not advisable, to go from one side of Dubai’s Interchange 2 to the other on foot. Encircled by ramps, the inner landscape is visual amenity accessed only by maintenance crew.
Sooner or later, the traffic has to come back down to earth where it creates local congestion and obstructs pedestrian movement. Whether Dubai or Shanghai, this happens when formerly high-speed traffic has to enter a low-speed system regulated by traffic signals. This is the West Nanjing Road exit ramp of the above-mentioned Yan’an Elevated. Traffic’s not backing up but, at peak hours and seeminglyrandom times during the evening, the surface traffic lights make it a long wait to exit the expressway and enter the local traffic system.
Even when there’s no backing-up, traffic still has to disperse from the exit points and cause local congestion because those exit points won’t be the final destination. This is one problem. Having many exit ramps will increase the expressway throughput but disrupt local traffic and having too few will make the expressway less efficient. It’s not much good racing from one end of town to the other if the final 300 metres is going to take the same amount of time because of congestion, or if the ramp closest to your destination is still some distance from where you want to be. There’s also the not insignificant problem of the amount of space taken up by exit ramps. How these problems were solved in LC’s 1931 Plan Obus was never made clear but then, despite the romantic depiction of speed, little of the traffic would have been thru traffic.
Diversion: It would have made more sense to have the turnaround ramps go down to the level below where they could also function as combined entrance/exit for the car park and a driveway for local access. However, this would mean that exiting the car park would mean having to go back into town unless there is a turnaround in the other direction. It wouldn’t be possible to get in your car and speed along the top to visit someone living further along. Stacking lower level access ramps beneath these turnaround ramps won’t help if you do want to go back into town as you’d still need to be on the other side of the road to use them. The only way around this is to have a turnaround further down the road, meaning you’d have to pass your destination entrance (with the car park entrance), U-turn at the next turnaround and then return to the one you just passed to go down a level and eventually make your way home. It would now be easy to visit your friend up the road – assuming another turnaround past where they live.
The only way around this is to have a ramp down to lower level and then a ramp up from the lower level, on both sides of the road, and as often as possible otherwise traffic will merely be shifted from the fast level to the slow level. Elevated roads don’t really make much sense when every point along them is a final destination for someone.
It’s no clearer in this 2020 student reworking for Hong Kong, although it looks like there’s domestic parking on the elevated road that’s essentially the elevated driveway of the original. Still, as the last sentence of the text states, better that “nature can flow underneath” than the space be taken up by either a building or a road. This is a separate problem.
While we’re talking about roads atop buildings, the Fiat factory building famously had an elevated road (with banked corners!) but was neither proposed or implemented to solve problems of traffic and access.
And then there was this elevated road that happens to be above water, and which can only be a two-tier traffic system with high-speed through traffic on top and low-speed local traffic along a very long driveway through the car park below.
The problems of the implied traffic system of Plan Obus are the same problems all elevated roads have – the problem of getting onto them and off them, and the problem of getting onto and off them at the place you want to. The obvious contradictions are that we want fast, cross-town traffic, smooth-flowing local traffic, and a seamless transition between the two. Self-driving automobiles won’t solve this because there’ll still need to be a transition between high-speed and low-speed traffic systems. It’s just exchanging one type of autonomous vehicle for another, without any shared system monitoring and controlling the big picture. This is Hyundai’s proposal.
It looks like the pod-buses take you only so far and then your personal pod takes you the remaining distance. All this would be centrally monitored and controlled much like a light rail network and the pods would presumably be available for re-use by others, or perhaps autonomously collected and repositioned at points of demand. It could work. It also seems to work to isolate people as much as possible. The buses don’t look much fun. How they will feel was already imagined in 1962.
The bigger problem with the Hyundai proposal is that it’s still a conventional road separating two sides of a street and, sooner or later, we’re all going to have to get out and walk. Mountainous places such as Hong Kong and Chongqing are less attached to the ground. Hong Kong has its network of elevated pedestrian streets, as well as buildings that aren’t entered on level one. Chongqing has bridges between buildings 65m above the ground, one instance where a light rail line passes through a building and, unusually for China, rooftop parking and access. [ref.]
This all seems to suggest that roads and building access are better off on the tops of buildings and the urban landscape allowed to sort itself out at ground level between or, if you must, under buildings. We don’t really have an image of what this will look like. We can’t keep returning to Mario Chiattone’s 1914 Futurist City or Fritz Lang’s 1927 film Metropolis for inspiration. The ground level in both instances doesn’t look like a good place to be.
The 2012 Total Recall remake did the high-speed stuff well but I seem to remember that getting off the elevated road was a problem even for anti-gravity self-driving automobiles.
Right now, there doesn’t seem to be anything midway between the totally autonomous self-driving vehicles currently being promoted, and a fully controlled mini light-rail system such as at London’s Heathrow Terminal 5.
The experimental autonomous vehicle system at Abu Dhabi’s Masdar seems like a happy medium, even if it largely operates in the unglamorous space beneath buildings in the “proof-of-concept” first stage of the city. The plan was for the entire city of Masdar to be elevated to make way for this transportation system that hogs the surface so the new raised “ground” level would be free for pedestrians. It was dodgy logic and, post-2008, it was the extensions to the city that came down to earth.
Putting the roads in the air makes a bit more sense than putting an entire city five metres up. If all transportation were elevated and buildings entered from the top, then perhaps we might have a better idea what we want the ground level spaces between buildings to be, whether the buildings are raised or not. These days, we don’t expect our cities or the urban economy to be so dependent on individuals getting from one place to another in as little time as possible. It seems more important that deliveries do. Designing our cities to support inter-city and urban infrastructure so that high net-worth individuals can zip from place to place to have value-added breakfast and lunch meetings might not be what the rest of us need.