Monitoring Informs Drivers for Weight Restricted Bridge
By monitoring vehicles crossing the Marlow Bridge, James Fisher Strainstall (JF Strainstall) have informed the bridge management for overweight and over-width vehicles
- Automatic Number Plate Recognition
- 4no laser distance gauges
- Automated on-site analysis
- Driver illuminated information boards
- Entirely battery operated
- Education to public users
Marlow Bridge in Buckinghamshire is a Grade I Listed Building, opened in 1832 and is one of only two remaining suspension bridges in the world designed by William Tierney Clark, understudy to both Thomas Telford and John Rennie.
Having been substantially restored in 1956-7 the bridge now has a 3 tonne weight limit and a width limitation of 2.0 metres to passing vehicles, controlled by narrow spaced bollards. Buckinghamshire County Council suspected vehicles were contravening the limitations and some drivers were potentially unaware they were doing so.
JF Strainstall were contracted to provide live vehicle monitoring, measuring vehicle weights and widths, while actively informing the passing drivers.
JF Strainstall's solution involved use of:
- Automated number plate recognition (ANPR)
- Laser measurements of vehicle widths while passing
Live measurements and data collected real-time from DVLA are analysed on site and, where necessary, gives illuminated display for driver awareness.
No electrical power supply was readily available on site, so JF Strainstall optimised the system to run on minimal energy draw and use battery supplies, remaining reliable even in cold weather.
Communication by mobile phone signal and collecting third party data from DVLA was nothing new to JF Strainstall, but the phone signal proved unreliable from this location and the time lag hindered the ability to display on the illuminated sign before vehicles had driven past. By improving the communication channels and innovations in the processing sequence, JF Strainstall reduced the delay from 6 seconds to under 1 second achieving the real-time warning requirements.
JF Strainstall recorded over 27,000 contraventions to the vehicle restrictions in just the first month, providing information to Buckinghamshire County Council. Measurement of the proximity of every passing vehicle to the bollards has informed the Council’s engineers of the patterns in driver movements and will determine potential adjustments to bollard positioning to better assist with enforcing the restrictions without hindering other drivers.
Trends can be seen in the passing vehicles which might be assumed acceptable but are not, especially larger vans and some bigger family cars.
The Council were able to determine that the information was successfully reaching the public when queries started coming from drivers warned by the illuminated displays – some of which had used the bridge in the same vehicle for several years previously.
It is hoped that vehicle numbers contravening the restrictions will continue to fall, as drivers are now more conscious.
By collecting vehicle information in real-time and displaying formation to drivers, the road users are better informed of the limitations on this iconic bridge