Application of UK Roundabout Technology at North American sites.

1. Insert the title of your presentation here US application/calibration of UK roundabout technology Presented by Name HereJob Title - Date

2. UK Roundabout Technology TRL conducted extensive research in the 1950’s and 1960’s resulting in the “yield at entry” rule used to navigate and also differentiate a roundabout from other forms of intersection. TRL subsequently spent 12 years researching capacity relationships at roundabouts and delivered the results to Traffic Engineers through ARCADY. ARCADY has been specified as the sole software for analysis of priority roundabout design in the UK since 1981. TRL is a non profit re-distributing research organisation recognised worldwide. As such ARCADY is UK Roundabout Technology. Copyright TRL

3. Level of Service Output in ARCADY 7 for each leg Directly based on queuing delay Data can be displayed in multiple formats Copyright TRL

4. Calibration What is being calibrated? Unusual geometry? Driver behaviour? Population demographics? Signage / markings / clarity? Prevailing weather conditions? Road surface? Origin / destination patterns Local knowledge? Local? Regional? National? Continental? Global? Driver confidence of roundabout navigation There has never been any attempt in the UK to derive correction factors for entire regions. ALWAYS SITE-SPECIFIC ONLY. Copyright TRL

5. Calibration facilities in ARCADY:1. CAPACITY SCALING This scales the entire capacity (per leg) Direct OR percentage Example: ARCADY prediction for capacity of Leg 1 = 1800 PCE/hr Observed entry saturation flow for Leg 1 = 1980 PCE/hr IF you believe that the difference is due to one of the reasons listed earlier and NOT due to mistakes in data entry, then: Enter capacity scaling factor of 110% ARCADY result will then appear as 1800 * 110% = 1980 PCE/hr and so is calibrated according to site observations Copyright TRL

6. Calibration facilities in ARCADY:1. CAPACITY SCALING (continued) This assumption requires engineering judgement Advantage is that it can be used to take into account ANY effect, no matter how complex the junction. It is applied towards the END of the modelling process, as a final adjustment This is intuitively easy to understand NB. It is possible to scale capacity for a roundabout network or separately for each leg which can prove more accurate in application Copyright TRL

7. Calibration facilities in ARCADY:1. INTERCEPT CORRECTION Traditional way of adjusting ARCADY results Relies on adjusting the INTERCEPT of the Qe-Qc relationship (preserving the SLOPE) The INTERCEPT is the max entry flow for a GIVEN set of geometries I.e., SITE-SPECIFIC Correction is based on observations of the intersection May be possible to derive an overall regional or national correction factor based on an average of many intersections Copyright TRL

8. Calibration facilities in ARCADY:1. INTERCEPT CORRECTION (continued) Advantages of Intercept Correction: Traditional method Well established (First introduced in very early versions of ARCADY) Reliable Disadvantages of Intercept Correction: Applied early on in the modelling process Copyright TRL

9. Calibration facilities in ARCADY Intercept Correction Copyright TRL

10. Calibration facilities in ARCADY What if Qe-Qc is not a linear relationship? Can use Capacity Scaling but must decide whether to implement as a % scaling, or a direct scaling Research continues so facilities for both options exist Copyright TRL

11. Copyright TRL Thank You North American Calibration of UK Roundabout Technology Mike Hutt/ Graham Burtenshaw Transportation – Traffic TRL United Kingdom www.trl.co.uk mhutt@trl.co.uk +44 134 477 0512