There are no really steep hills on the Hertfordshire Greenways route. The steepest / longest grades come after St Albans and before you get on the Nickey Line in Hemel Hempstead. There is a long climb on the way up to Bedmond and a couple of longish climbs up to Bovingdon from Kings Langley. The steepest gradient is around 12% in that area. It probably feels stiff as it is after the gentle grades on the Alban Way. Once on the Nickey Line the route returns to gentle gradients again.
I need to pop out and take some photos of the final stages of the Hertfordshire Greenways 100 and get them on the website. I have rerouted it at no extra distance to come by the Stevenage pub the Four Minute Mile 200 finishes at. Thus later 100 finishers can mix with the faster 200 finishers. If anything the finishing lanes of the 100 are even quieter than my original choice. Not that either are busy.
The steepest grade on the Four Minute Mile is 20% plus a few 13-15% hills later on. The 20% hill is not for very long as I rerouted to avoid the full straight up climb that the original route had. Optionally you can still climb the full length of the 20% hill should you choose.
This is around some of the steeper lanes encountered in the Chilterns (on the Four Minute Mile 200).
If anyone would like to join me on the helpers ride / route check of the Four Minute Mile 200 on Sat Sept 15th and can sit in a pub late afternoon on Sat Sept 22nd waiting for riders; let me know.