Traffic into south east London this week faced a month of chaos after a hole opened up in the A2 at Blackheath.
Suspected cause of the 6m diameter hole that appeared in Blackheath Hill Road on 7 April is the collapse of old chalk workings 10m beneath the carriageway.
The dual carrigeway road, which is a major artery for traffic into and out of London, was immediately closed in both directions and 37 households were evacuated by Greenwich Borough Council as a precaution.
Motorists still face delays of up to an hour and are being urged to avoid the area completely. Meanwhile, site investigation by Transport for London ( TfL) has been hampered by safety concerns.
Engineers from TfL and consultant Parkman - which maintains the road on TfL's behalf - were immediately on the scene. But continued settlement of the carriageway meant that for eight days the area was not deemed safe enough for an initial investigation using ground radar to begin.
The ground radar indicated that further 'soft spots' may exist beneath the carriageway, and a further geotechnical inspection using cores and ground probes will be needed before the area is considered safe for investigation using heavier plant.
Only then can full depth probing take place to allow engineers to investigate the root cause of the collapse, and to find a solution.
If collapsed chalk workings are confirmed as the cause, a likely solution will be to fill the void with grout. But the extent of the void is unknown, and it is feared that use of large quantities of grout would lead to environmental protests which could further delay reopening of the road.