Cambridge (compromise) Kerb

This article was published in 2015, in Newsletter 123.

Of course all life is a compromise, especially for those of us who strive for unattainable ideals.

The ideal as achieved on parts of Huntingdon Road is a cycle lane truly segregated by a double 100mm raised kerb, where all but the most cautious parents would allow their competent five-year-old to cycle. Unfortunately, there are many other constraints that make such segregated lanes difficult, expensive or impossible to retro-fit to all our existing urban roads.

Part cross-section of road at the kerb (Diagrammatic only – not to scale).
Image as described adjacent

I’ve started so I’d better begin. The Cambridge Kerb is a compromise that helps better delimit a ‘softly’ segregated cycle lane from that part of the carriageway designed for all traffic. It is a concrete kerb section that has been constructed with a slight slope over a 150mm (6″) width. This is sufficient to make it clear, especially with a well-contrasting surface to the kerbed cycle lane, that drivers of motor vehicles should not enter, yet provides little danger to those cycles who need to cross, whilst in exceptional circumstances allowing a motor vehicle to cross.

Although with ‘traditional’ Mandatory Cycle Lanes motor vehicles MUST not enter, there are exceptions, one good case being to permit the passage of an emergency vehicle. On Hills Road the construction of the improved cycle lanes results in the narrowing of the normal lanes and this is an area where at peak times queues can exist in both directions. Hard segregated lanes would NOT be acceptable for the emergency services on this stretch, as it could seriously impede the progress of such vital traffic.

In some places ‘semi’ hard segregation is used but for those on cycles who wish to leave or join across a busy road, say from a private drive or minor road opposite, it can be risky. One road in Oxford had alternate ‘kerb and no kerb’, and in the dark and wet with busy traffic it proved difficult for inexperienced riders to negotiate the obstacle course.

New cycle lane layout on Hills Road.
Image as described adjacent

I’ve long been a believer in the 3 ‘E’s of Education, Enforcement and Engineering. With the more normal Mandatory Cycle Lane with a 150mm white line, both Education (even of police!) and Enforcement seem to fail, and the government seems to think the extra powers, which it could make available under the Traffic Management Act 2004, are simply a ‘War on the Motorist’.

Cambridge Kerbs look like a good engineering compromise, but only time will tell if this passive education will lead to better compliance. On almost the first day of operation, a two-way hard segregated cycle super-highway in London was obstructed by a Tesco delivery vehicle!

As with all engineering the devil is in the detail. To be safe and effective the upstand between the normal carriageway and the Cambridge Kerb must be minimal. There are standards for ‘flush’ and ‘dropped’ kerbs. Dropped kerbs should have an upstand of over 10mm which then enables the disabled to easily recognise the carriageway edge. Such an upstand could cause a tumble for someone approaching at an acute angle, especially in wet weather.

For such locations the specification should be ‘flush’ with an upstand not exceeding 3mm (the county council used to quote that in the ‘Network Management Plan’). I think there are workmanship issues at some locations on this new stretch.

One advantage of such soft segregated cycle facilities is that the construction costs are far lower that for a road widening or bus lane.

I like this approach for a section of road where hard segregation would be difficult. The Cambridge Kerb is different and should get respect from the majority of motor vehicle drivers. Perhaps the ‘Pavement Parking Bill’, soon to go before Parliament, needs a clause to cover such lanes?

I’m still unsure how best to deal with ‘signs and lines’ here. A Traffic Regulation Order and a 150mm line painted on the kerb would be clear to me, but to who else? I don’t have shares in the companies that make yellow paint, otherwise I might recommend double yellow lines with, at the least, single unloading ‘tick’ marks. And where do you put the yellow lines? In the main carriageway, or in the cycle lane? Perhaps when you read this a decision will have been made.

Jim Chisholm