My proposed project duration is shorter than two years long. Is it allowable to submit a one-year project instead of for two years?

Yes, the RFP references funding durations for up to two years. It does not mandate that projects must be two years in duration. However, in terms of future eligibility, if you receive a CUSE grant as the leading PI in 2018, you cannot apply for a second CUSE grant until 2020 (i.e.- 2 years after receiving initial CUSE grant), even if the project is less than 2 years in duration.