Yes you can, just follow these steps:
On Mobile:
- From the side menu select My Trips
- Next select Manage Trips
- Choose the trips you want to combine
- Select Combine then Continue
- Create a name for your trip and save
On Web:
- Click the Actions menu on your trip card
- Select Combine Trips
- Choose the trips that will be merged and press Combine
- Create a name for your trip