I dunno', I've been going into Cambridge 1-2 month for work for the past 4 years and it seems to be getting worse with each passing year. I think it is due to a number of factors including more students with cars, more people working untraditional 9-5 hours and my personal theory being people on their phones and over devices. If everybody making a call, text or searching for something slows themselves down by 2-3 seconds because of their actions, think of the cumulative effect of thousands of people doing it.