Does the state of the road system really dictate what the railway can run? If so, there are countless issues around the country that would prevent the existing service from running. let alone any increases!
Yes it does when the Railway interface affects the Road System significantly. In this case a very busy road intersects a quieter Railway line and as importantly a major Road intersection (A217/A25) is affected by the Railway too.
Far more people will be inconvenienced by the extra trains than will travel on them. This is an additional service not a current service so the reference to existing issues is not relevant here.
Traffic on North Downs Line is (in my opinion) not significant enough to justify increase to 3 trains per hour between Guildford and Gatwick although the service is very valuable to local communities. That is why I suggested that 2 per hour to Gatwick only, in an alternating pattern between Guildford and Redhill. That is Shalford, Chilworth and Gomshall for one train and Dorking West and Betchworth on the other train. All services calling at Dorking Deepdene, Reigate and Redhill.
Obviously this increases journey time by around 10 minutes but it is a community service rather than a fast train to the airport and I can't imagine Airport passengers using it once or twice a year would be put off by an extra 10 minutes - it's more about not carrying suitcases everywhere.