Don't most injuries on Worthing's roads happen on the A-roads which won't be included?

No. The table here shows that only 44% of all injury collisions in the last six years were on A-roads. The majority are on B, C or unclassified roads – precisely where the campaign is arguing for 20mph limits. If you look at the data for children the figure is even higher – 67% of injuries to children occur on B, C or unclassified roads.

There are many other reasons for 20mph limits on residential roads – encouraging walking/cycling, reducing air and noise pollution and creating better quality of life, but the data on injuries alone would justify it.