A large majority in the European Parliament has approved new rules to make big lorries safer for other road users and more fuel-efficient.
If national governments back the changes, lorries will have to have bigger windows and rounder fronts - rather than the standard "brick" design used for drivers' cabs now.
New designs will tackle the driver's "blind spot", blamed for many deaths.
Groups representing cyclists have urged the UK government to back the changes.
The proposals were backed by 570 MEPs, with 88 against.
London Mayor Boris Johnson, who launched a popular cycle hire scheme in the capital, says he is worried the UK government may oppose the changes.
The draft legislation says "a new cab profile will also contribute to improving road safety by reducing the blind spot in the driver's vision, including under the windscreen and to the side of the vehicle, which should help save the lives of many vulnerable road users such as pedestrians or cyclists".
"The new cab profile should therefore, after an appropriate transitional period, become mandatory. This new profile should also incorporate energy absorption structures in the event of a collision."
A more aerodynamic shape at the front would also improve fuel-efficiency, supporters of the legislation argue.
The European Cyclists' Federation says heavy goods vehicles are involved in 18% of fatal accidents on Europe's roads, which cost thousands of lives in the EU every year.
British Labour MEP Brian Simpson, one of the chief negotiators on the issue, said "we need to make sure that cabs are designed to give drivers a clear view", noting that "lorries are involved in a disproportionately large number of cycle deaths".
If the new design features are approved by the 28 member states' governments they will become compulsory for manufacturers seven years after the new EU directive takes effect.
EU directives do not become law immediately - countries have two years to "transpose" them into national law, after they are published in the EU official gazette.
A British Liberal Democrat campaigner on the issue, Phil Bennion MEP, called the vote a "victory for all the campaigners in the UK who have worked so hard to bring about these life-saving changes to lorry design".
He said he was confident the changes would get government approval later this year, after the May European elections.
Manufacturers will be able to make bigger lorries provided the extra space is used to incorporate safety and aerodynamic features.