TRL were commissioned by Transport for London (TfL) to test a wide variety of innovative cycle signals and layouts, which involved undertaking a range of trials with cyclists and other road users. Four sub-trials were conducted to investigate the reactions of road users to Low Level Cycle Signals (LLCS) at a specially constructed typical ‘urban’ four-arm junction built at TRL’s test track. In the fourth of the four trials the LLCS were accompanied by three different cycle reservoir depths of 5m, 7.5m and 10m. The LLCS were positioned on a separate pole to the standard traffic signals, with the LLCS being at the second stop line and the main signals being at the first stop line. This junction layout was trialled both with and without an ‘early release’ for cyclists ahead of the vehicle traffic. Trials were conducted over fifteen days with a total of 1,290 participants for two different road user groups (cyclists and car drivers). In the cycle trial two group sizes were tested: a ‘small group’ of eight cyclists and a ‘large group’ of 16 cyclists. These findings suggested that the following reservoir depths may be considered for a junction with a one-lane approach: a cycle reservoir between 5m and 7.5m deep when the required space is 8 to 13 cyclists; a cycle reservoir greater than 7.5m deep when the required space is 13 or more cyclists. A rule of thumb is therefore 1.7 cyclists per metre of reservoir depth for a one-lane approach.

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