Definition – This expression refers to an opportunity to do something that will only last for a short time and needs to be taken advantage of quickly.
Relevance to SUMP – In the context of SUMP development and implementation, a window of opportunity is said to open when the political will and resources to accelerate planning or implementation of one or more measures are unusually high. The window of opportunity may be caused by external events that make sustainable mobility
a high profile political topic, such as a period of very bad air quality caused by pollution. Windows of opportunity may also be created through events organised by a public authority, for instance a ‘car free day’ that raises awareness of sustainable modes of transport and proves to be very popular.
Source: Collins Dictionary (online)