The introduction of 20mph speed limits in residential streets is to be reviewed by the government, according to reports.
The research into the zones, which have been introduced across Waltham Forest and Redbridge, will focus on the impact on collisions, casualties and air quality.
It is claimed the zones improve road safety, but there are concerns they coould increase pollution.
London University Professor Michael Maher will lead the review, according to the BBC.
The announcement came in a response to a question by Green MP Caroline Lucas by Transport Minister Robert Goodwill.
He rejected calls for 20mph to be the default speed limit, adding councils are best placed to consider the option.