• Xiaofan Zhang

CamCross: An innovative concept for the Cambridge Autonomous Metro - Part 1

I’m Xiaofan, and last year, as part of my Master’s at the University of Cambridge, I created a conceptual systems design for the Cambridge Autonomous Metro (CAM) – a major public transit initiative aimed at creating a new form of public transport to alleviate congestion across Cambridgeshire. Before this, I led the team that built one of the World’s most efficient electric family cars.


In this blog, I will introduce my concept for the CAM, called CamCross, and explain the philosophy that influenced my design decisions. This is the first blog post in a series that I will be releasing over the next few weeks. In each of the upcoming blogs, I will share detailed explanations of the system elements including, vehicle concept, novel station designs, my proposed network layout, and the concept of operations.


Where CamCross is unique is that it uses relatively small, low capacity autonomous vehicles (~20 passengers) to create a demand-responsive rapid transit system that can cope with relatively high passenger flows. connecting Cambridge with the surrounding satellite towns. Its novel concept of operations would offer faster travel and higher convenience than similar journeys taken by private car.

My concept vehicle for the Cambridge Autonomous Metro

CamCross has significantly cheaper infrastructure costs and operational costs than alternatives such as light rail and current proposals for a tram-like CAM. CamCross could likely become profitable via the farebox alone due to its low cost. This is notable, as mass transit systems typically rely upon significant public subsidy.


Some of my work was included as part of the CAM Technical Advisory Committee’s (CAM TAC) report advocating for more affordable and innovative approaches to the system’s design – a report that was called a “game-changer” by the Mayor.


Why I am writing this blog?

In September 2020, I founded CamCross Mobility Limited with my friend Johannes Theron and built a consortium with 9 partners (including urban designers, electric vehicle engineers, transport planners, etc.) to compete for funding to undertake 3 months of conceptual design work and develop these ideas further.

CamCross Mobility Logo - Inspired by my station design

Our partners included several local companies who were open-minded to exploring innovative approaches and very passionate about improving the region. Sadly, we were eliminated from the process before we had a chance to present these ideas which was a real shame. The CAM project is rapidly moving on with other companies currently working on concepts. I wish them luck in the project and am excited to see what they produce.


I am now directing my focus onto some other projects in the energy field, but I am still passionate about the topic, so I did not want these ideas to die with my involvement.

I thought I would share my concept with the hopes that it will spark a discussion and further thinking, either in Cambridge or beyond. A lot of these ideas are somewhat underdeveloped given the limited time I had, and would likely have changed significantly as we did more research and design work. I am curious to see what the collective power of the internet thinks.


I would like to thank Professor John Miles (my project Supervisor and long-term innovator in this field), Dr. David Cleevely, and Dr. David Braben from the CAM TAC. This work would not have been possible without their support and built heavily upon their ideas for such a system.


Why is a new public transit network needed in Cambridge?

Private cars are the dominant vehicle of choice for commuters travelling between Cambridge and its surrounding satellite towns. However, the low-capacity road network of the medieval town is overstretched, with Cambridge being named the congestion capital of the UK as the average driver spends 23 days a year sitting in traffic – a depressing statistic. This is almost equivalent to the statutory annual leave entitlement for UK employees of 28 days– imagine if you could reclaim this time!

Typical road traffic map at 8 am on Tuesdays within Cambridge with key sites of employment labelled.

Cambridge is one of the fastest-growing cities in the UK and is home to many growing technology companies. There are already many plans to build new major residential and commercial properties across the region – congestion will only worsen without a solution. This will likely disproportionately affect workers with lower incomes as rising house prices within the city mean that they often live further out.


Map showing planned new builds in the 2018 Local Plan

Current forms of public transit (buses/ rail) struggle to provide sufficient flexibility and convenience to compete with private car usage. As such, there is a drive from the Cambridgeshire and Peterborough Combined Authority (CPCA) to develop an “innovative world-class public transport system” called the Cambridge Autonomous Metro. The current target launch date for this is in 2029.


A well-designed transit system could reshape the area and significantly improve the quality of life for all residents across the region – this was what really excited me about the project. Furthermore, this issue is not unique to Cambridge, as there are many other small cities across the country (and abroad) struggling with similar issues.


The Philosophy behind CamCross

A new transit system must offer a better journey than a private car to be an attractive alternative. Cars offer high convenience and flexibility at an affordable price, particularly given the dispersed nature of residential properties in rural and semi-rural areas.

The following design aims for CamCross were adopted (in order of importance).


1. Reliable and predictable: The system should not be susceptible to road traffic (unlike road-going buses) and offer dependable journey times.


2. Frequent: The system should be frequent enough so that timetables are not required (e.g. departures at least every 5 minutes) – this allows similar flexibility to a private car.


3. Low fare cost (but remaining economically feasible): Fares should be cheap (less than £5 return per day) to ensure that it is affordable for all and comparable to the cost of fuel.

However, fare revenue would ideally be sufficient to fund any loans required to build any new infrastructure required.


4. Fast: Total journey times (measured from door to door) should ideally be shorter than equivalent car journeys, with minimal stops for each journey.


5. Attractive and convenient: The commuter experience should be desirable be with a minimal number of changes, and convenient first/last-mile solutions integrated into the system design. Vehicles and stations should be modern and comfortable, with WiFi and other amenities.


To deliver upon these aims, particularly No.1, a closed system is required with new infrastructure where vehicles are isolated from conventional road traffic and associated congestion. In the long run, this could allow large areas of Cambridge City to become fully pedestrianised with CamCross vehicles running underground.

Cambridge guided busway - the World's longest guided busway.

Building new infrastructure such as segregated pathways and underground tunnels is very expensive but appears to be unavoidable in Cambridge. Thus, the infrastructure costs will dominate the costs of any solution and all efforts should be taken to minimise them.


Why is innovative thinking required? Can’t Cambridge just build a Light Rail System?


Despite its rapid growth, Cambridge is still a fairly small city and unlikely to produce the demand required for conventional mass transit systems to be affordable. For example, conventional Light Rail requires passenger flows of around 5000pphd (passengers per hour per direction) to be economically feasible – passenger flows in Cambridge are likely to be closer to 2000-3000pphd. The income from passenger fares would not be sufficient to fund the high infrastructure costs, and therefore it would require high public subsidies.

Inner West Light Rail in Sydney, Australia

Recent developments with automotive technologies (Autonomous Vehicles and Battery Electric Vehicles) means novel vehicle concepts can be created and demand-responsive services can be deployed at an affordable cost. What’s more, running the vehicles within a closed network makes the technical challenges of autonomous driving significantly easier. This is important as it means that CamCross could be delivered with technology that is already commercially available today.


What's wrong with the old proposals for the CAM?


The existing thinking around the CAM centred around using large autonomous, high-capacity (possibly over 150 passengers per vehicle) rubber-tired trams. These would operate on purpose-built pathways running at grade through rural areas and in 12km of two-way tunnels underneath the City (the high building density within the city rules out building pathways at grade within the city).

Visualisation of the Cambridge Autonomous Metro

However, the types of vehicles that had been proposed require expensive fixed infrastructure (wide bore tunnels and large underground stations in particular) pushing the projected cost to £4bn, a figure that is unlikely to be economically feasible even with ambitious estimates for future demand in the region. Moreover, the infrastructure and other system elements proposed are too inflexible to take advantage of the rapid technological progress in automotive and information control systems that will be made over the lifetime of the system (decades at least). The report produced by the CAM TAC explores this in detail.

Small autonomous pod

I also explored the potential of using very low capacity vehicles (less than 6 passengers per vehicle and as low as one- or two-seater vehicles) to deliver highly bespoke journeys. I’ve seen systems like this proposed in various guises for other locations, but I found these to be impractical for a system as large as CamCross. A very large number of vehicles were required, increasing the cost significantly, and I found that the system was likely to become overwhelmed during peak demand, particularly at choke points such as the underground stations and tunnels. There was a high likelihood of simply creating congestion underground with so many vehicles.


CamCross – My concept for the Cambridge Autonomous Metro


What is special about the CamCross concept?

CamCross uses small, low capacity vehicles which has two key benefits: significantly reducing the cost of the infrastructure and allowing the system to be very flexible depending on the demand.


A bespoke vehicle would be created with a small cross-section (the UK is a great place to develop and build these vehicles given the wealth of expertise within EV design, and low volume high-value manufacturing). This means smaller and cheaper infrastructure (tunnels, pathways, and stations) can be used, keeping costs affordable. I have designed an illustrative concept vehicle for this.

Convoying vehicles to achieve high passenger flows

In busy areas such as the centre of Cambridge, these vehicles can effectively run like a train by convoying to cope with large passenger numbers. In quieter portions of the network, they would run as individual vehicles allowing a service to be offered every few minutes without the vehicles running nearly empty. This is particularly important for providing a good connection for rural and semi-rural residential areas to the network.

CamCross vehicle concept

NB: the mannequins in the model are all 95th percentile men, which is why it might look a little cramped at the moment.


Passengers with similar journeys could also be grouped into the same vehicle, reducing the number of stops that each commuter makes along their journey. This helps to cut down overall journey length and minimises the number of vehicle changes a passenger needs to take.


Is it just a vehicle concept or is there more to the design?


Whilst the vehicle concept is important, the rest of the system is equally crucial in allowing CamCross to deliver a reliable, frequent, cheap, fast, and attractive service.

Current proposed network map - I'll share mine in an upcoming blog

To fully take advantage of the flexibility offered by small vehicles required rethinking many other elements of the system. I reworked the network layout to better connect key population areas whilst reducing the length of costly tunnels. I also created a concept for a unique underground station that allows for a very high passenger capacity, vehicles to easily change between lines, and space for retail or bike storage. The design manages to achieve this within a small footprint, allowing the costs to be kept modest.

Central underground station diagram
Side view of the central underground station

How would CamCross journeys compare to a car? And how much would it cost the public in subsidies?


I found that CamCross could deliver a high-frequency service to all stations within the network at an affordable cost. The journeys I tested on my model were sufficiently fast to rival journey times in a car, even during off-peak times.


What is especially exciting about CamCross is that revenues from the fare-box alone could cover the cost of building and operating the system so it would likely require little to no public subsidy.


What's next for these blogs?

I look forward to sharing my explanations behind all of these system elements over the next few weeks. Next week I'll be looking into the design decisions behind my vehicle concept.


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Thanks for reading! I hope you found it interesting! :)



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