  The arrival time of coronal mass ejections (CMEs) in the vicinity of the
Earth is one of the most important parameters in determining space weather. We
have used a new approach to predicting this parameter. First, in our study, we
have introduced a new definition of the speed of ejection. It can be considered
as the maximum speed that the CME achieves during the expansion into the
interplanetary medium. Additionally, in our research we have used not only
observations from the SOlar and Heliospheric Observatory (SOHO) spacecraft but
also from Solar TErrestrial RElations Observatory (STEREO) spacecrafts. We
focus on halo and partial halo CMEs during the ascending phase of Solar Cycle
24. During this period the STEREO spacecraft were in quadrature position in
relation to the Earth. We demonstrated that these conditions of the STEREO
observations can be crucial for an accurate determination of the transit times
(TTs) of CMEs to the Earth. In our research we defined a new initial velocity
of the CME, the maximum velocity determined from the velocity profiles obtained
from a moving linear fit to five consecutive height time points. This new
approach can be important from the point of view of space weather as the new
parameter is highly correlated with the final velocity of ICMEs. It allows one
to predict the TTs with the same accuracy as previous models. However, what is
more important is the fact that the new approach has radically reduced the
maximum TT estimation errors to 29 hours. Previous studies determined the TT
with a maximum error equal to 50 hours.
