Transport for London (TfL) brought the case against the telecommunications giant following the incident involving works to Bishopsgate during August 2017.
Westminster Magistrates Court heard on 28 March how BT failed to properly sign and guard the work area. They had also used the wrong traffic management methods.
Despite repeated demands by TfL, BT also failed to take actions to improve the situation, leading to unsafe conditions for road users, pedestrians and cyclists.
BT pleaded guilty to the unsafe execution of streetworks with significant risk to public safety at Westminster Magistrates Court and was fined £90,000 and ordered to pay a further £3,394 in court costs.
In sentencing, the District Judge said: "There is clearly a disconnect between BT and its contractors, consistently resulting in a number of these breaches, which must be fixed by BT to avoid future offences. It took over a day for BT to rectify these faults despite the works taking place in a busy part of the City of London with substantial impact on traffic. The response was unacceptably slow in my view and I hope that is reflected in my sentence."
Glynn Barton, TfL's director of network management, said: "The safety of the public and workers should be top priority when undertaking roadworks.
"It is absolutely vital that companies such as BT ensure safety on site and we will always push for the strongest possible action against those that put the public at risk," he added.
TfL points out in its press statement this is the second time in 12 months it has taken BT to court for unsafe working practices involving roadworks.
Unsafe work carried out on Streatham Hill, Lambeth on 1 March 2017 meant that pedestrians were able to walk ‘dangerously close to heavy plant and machinery’, says TfL.
A spokesperson from BT's telephone system maintenance division, Openreach, said: “We fully accept the Judge’s decision and we’re sorry that our safeguards were not up to scratch in these two cases.
“We carry out 3,500 projects like this every month across London and over 99 per cent of these are completed without incident.
“Safety of the public is absolutely paramount to us, and we’ve put further measures in place for our contractors to follow that we believe will prevent this happening in future," they added.