Due to the limitation of Cell-specific Reference Signals (CRS), the channel estimation for LTE downlink system is a challenging topic, especially for vehicular users at high speed suffering from severe fading. In this paper, an improved channel estimation method with downlink channel signaling aided detection is proposed for LTE downlink system. The considered specific signaling symbols include the Physical Control Format Indicator Channel (PCFICH) and the Physical Hybrid-ARQ Indicator Channel (PHICH). By traditional Least Square (LS) estimation and Wiener interpolation, the additional channel estimations by the above PCFICH and PHICH are combined with the results of CRS to obviously enhance the estimation accuracy, accordingly to improve system performance. The effectiveness of the proposal for different system bandwidths in LTE is analyzed, meanwhile the complexity is evaluated. Since each vehicular user assigned with several subcarriers can be regarded as a narrower bandwidth system, some numerical simulations are finally provided to verify the proposal, especially performance improvements for narrower bandwidth systems.