First of all Mukesh, you can never reach dehradun from Delhi in 2 hours.
Track from Delhi to Meerut is double. Then from Meerut to Saharanpur it is single lane. Saharanpur-Roorkee-Laksar track is double and electrified. While Laksar-Haridwar-Dehradun track is single.
There is scope in doubling Meerut-Saharanpur track and I think there is a proposal to do so also. For Laksar-Dehradun route, a large part of track pass through Rajaji National Park between Haridwar and Dehradun, so I think it is not beneficial to speed up trains. In this route all trains including...
more... Shatabdi Exp. runs at relatively low speed, due to fear of animals. Tunnels after Haridwar are also additional reasons.
Lalu announced a new track from Haridwar to Roorkee having Baba Ramdev's Patanjali Yogpeeth as station,few year ago. But now I don't think that it will turn into reality. But there is going to be a new track from Deoband to Roorkee, eliminating Saharanpur (also Tapri) on Delhi-Dehradun route. Survey and land acquisition has been done for this route.