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The Not-so-elevated Road

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The two main advantages of elevated roads come from them being elevated. One is that the land beneath them can be used for something else or even left as it is, and the other is that through traffic is not hindered by local traffic.

The main disadvantage of elevated roads is also due to them being elevated, as they require exit ramps to connect to the surface traffic and this causes problems. Two relate to the length of exit ramps and involve a trade-off between shorter exit ramps that less land, and longer ramps that will hold more vehicles waiting at traffic signals to enter the local traffic system. This suggests that elevated roads should not be too elevated. 

Two more problems relate to the number of exit ramps and also involve a trade-off between more exit ramps requiring more land to accommodate them but mean less surface congestion overall, and too few that will save land but concentrate vehicles around junctions likely to be some distance from the final destination. There’s no way around this – it will always happen when a high-speed traffic system connects to a low-speed traffic system. The only solutions are to either completely separate the two (as happens at airports and railway stations where a high-speed transport system meets a low-speed one), or merge them into one system and eliminate the difference. This suggests that high-speed cross-town travel is best left to rail networks.

If there’s the land to do it, a high-speed and a low-speed road system can merge by long entrance ramps and feeder lanes that provide autonomous drivers in autonomous vehicles the time to merge into a single high-speed flow. This works for entering a high speed system but exiting one will involve traffic signals sooner or later. Traffic signals impose a shared logic onto the two systems and merge the (formerly) high-speed traffic and the low-speed surface traffic by forcibly alternating the priority of the two streams. Drivers and their vehicles are not so autonomous anymore and so this sudden deprivation of autonomy is frustrating. 

The self-driving automobile removes much driver autonomy (a.k.a. the “burden” of driving) but then so does a chauffeur, or a taxi, whether piloted by a driver or some remotely controlled automated system. There are two types of self-driving vehicle Various object detection sensors allow autonomous vehicles to keep out of each other’s way as they proceed to their various destinations whereas connected vehicles are collectively and centrally controlled as part of a single flow. The personal pod system at Abu Dhabi’s showpiece Masdar City is a connected system where all you need do is state where you are and where you want to be.

Despite the automobile industry deciding that autonomous vehicles are what we want, I’m imagining a system of connected vehicles with an average size like the one above but with larger dedicated ones the size of a minibus pooling commuters or students.

“Capable of transporting up to 12 people, the Autonom Shuttle has a top speed of 25km/hr. The vehicle uses on-board cameras and sensors creating 3D and 2D “perception maps” to detect obstacles and their position relative to the vehicle. GPS technology further allows the vehicle to define its precise location, as well as V2X to communicate with traffic lights.” Arabian Business

The Kerbside Drop-off

Such a system needs no private automobile ownership or car parking. It would make the kerbside drop-off our main interface between building and vehicle but, spatially, how would that work? If streets are used exclusively for transportation, then what’s going to happen to the activities that historically lined streets? Much has already gone. The Hyundai concept transportation system I mentioned last week, still assumes a traditional city whereby transportation exists so that people can pass shops and services at ground level and offices and residences above. Its only advantage is that it could be implemented now if we wanted it to. [It’s essentially a double kerbside, with buses dropping off the pods into a “slip-road” pod lane before dropping off their passengers to a conventional footpath to finish their journey on foot.]

The vertical or horizontal configuration of any smart [ugh!], transportation system must work for residents, people shopping (at whatever shops are left to sell goods and services), workers (that still commute), students (for whatever education is still best conducted face-to-face) and deliveries. The Hyundai system would work because it maintains the same spatial relationships between housing, retail and commerce that have existed since the days of the horseless carriage, the horse & carriage, and the ox-drawn cart before that.

The commercial realization that persons travelling at speed in an automobile needed time to get excited about the products and services on sale just ahead first gave the world Googie architecture and the architectural realization that that buildings were signs gave us Post Modernism. But not everybody lives in America of the 1950s and 60s. Private car ownership is down, fuelling them and parking them is expensive, and even the idea that one can simply drive along a road to where you want to go and park there when you do seems like the past it is.

Such a culture still exists in places like Dubai where automobile ownership is high and most of life is spent indoors. Nevertheless, in the milder months, kerbside restaurants offer valet parking to encourage customers to eat outdoors along a street.

The 1950’s also gave us the suburban shopping mall that took shops and people from city streets and placed them in a traffic-free environment with pedestrian streets, events and plenty of places to sit and have a coffee or a meal while watching people go about their business. During opening hours.

It was a successful formula despite its known disadvantages of killing cities and encouraging car ownership. This next is a drop-off to what looks like a shopping mall with offices above.

I’ve done my time in taxi queues at shopping malls and airports but more recently, I’m usually waiting by a kerb somewhere for a Didi (the Chinese Über) to pick me up. Drop-offs function much like car parks in that they are used to change from a high-speed travel mode in some kind of vehicle, to the low-speed travel mode known as walking. Drop-offs don’t require private car ownership or much space whether pubic or private, and are suited for car pooling and all types of taxis no matter how they’re piloted.


In Hong Kong is Tai Koo Estate and, at its centre, the City Plaza shopping mall forms a podium for eight residential towers called Horizon Gardens.

Both retail and residential are still entered and serviced from traditional ground-level streets with pedestrians, private vehicles and commercial vehicles using the same street for different purposes. There are service entrances next to mall entrances next to residential block elevator lobbies. Despite pockets of amenity space, the streets are used mainly for access to the shopping mall and residences above.

Residents don’t look over these streets and individual retailers don’t target advertising to people moving along them. Even the more recent historic functions of the street no longer apply. This suggests that the street as we know it has outlived its usefulness.

While we’re in Hong Kong, it’s worth remembering how well the city’s system of elevated pedestrian walkways functions to shift people around the city and from mall to mall unhindered by surface traffic.

It’s often remarked that Hong Kong isn’t a ground-centric city. The relationship a level has with respect to the surface is simply not a useful concept for orientation. My first example is Exits A1, A2 and C1 at HKU Station. There’s one ground level stop between the train level and the university concourse level at ground level some way up.

The more relevant example is the drop-off access above Hong Kong’s Pacific Plaza mall. This is natural ground level as a historic tree has been retained.

This “ground” access level isn’t a bad place to be but, again, there’s very little reason to be there if not arriving by taxi.

This level leads directly to a hotel entrance, the apartments lobby, and escalators down to the mall.

Inside it’s three floors but, at the other end of the mall, the second floor links to a pedestrian footbridge a floor above ground level outside.

Putting it all together, this suggests that access roads should separate residential and retail/commercial uses, with retail and service below and residential, hotel and office buildings above. And that’s it. It’s easy enough to imagine this new configuration for a city. It doesn’t matter where natural ground level is.

Apart from spaces for vehicle charging, the access level is primarily for horizontal access to vertical access points. There are no private vehicles and no parking. The mall/city area below could look much like a conventional covered mall as in Hong Kong or Dubai.

It’s not rocket science. What I’m suggesting is only a magnification to urban scale of what you see above, with driverless pod vehicles on the access level and retail and services levels below. Spatially and functionally, it’s no different from Pacific Plaza.

Jon Jerde’s Namba Parks mall in Osaka, Japan shows us what this city might look like if it were configured as an open mall below an access road and with residential and other uses in towers above .

Jon Jerde’s Canal City mall in Hakata, Japan also shows us what a city might look like if it were designed around people being there, rather than around the means of getting them there.

The circular towers I made earlier, but I think it’ll look something like this. It can be as tight or open, or as regular or “parametric” as fashion and economy demand.

Elevating roads still makes sense because urban functions can be separated vertically into above and below. Now that we have the prospect of connected, driverless automobiles, the entire concept of using the same mode for both high-speed long-distance and low-speed local transport crumbles. Separating various zone of a city horizontally is always going to involve separating access to them vertically. Why elevate the roads in order for people to enter buildings at ground level only to take an elevator back up?

Thanks Mark!