The rapid penetration of intelligent transportation systems (ITS) into the conventional transportation infrastructure urgently calls for high spectral efficiency high reliability communication technology for vehicle-to-vehicle and vehicle-to-infrastructure (V2X) applications. Since orthogonal frequency division multiplexing (OFDM) is widely considered as a promising candidate for such applications, in this paper we propose a novel variation of OFDM for improved spectral efficiency as well as enhanced reliability in V2X channels with correlated frequency-selective fading and inevitable Doppler effects. Our proposed scheme is built upon a recently emerging technique termed as index modulated (IM-)OFDM. However, different from the existing localized subcarrier grouping, we propose interleaved subcarrier grouping. We then carry out analytical and simulated comparisons to demonstrate the merits of this new scheme in terms of both the bit error rate (BER) performance and the maximum achievable rate (MAR) of the overall system, in V2X channels.