Isolated incidents of violence have been reported between APC and SLPP supporters during the month-long campaign, with minor injuries and material damage.
Sierra Leone suffered a horrific 1991-2002 civil war, and memories of election violence from an earlier era often cause anxiety among the authorities at voting time.
Chinese controversy
Some question whether voters will lack transport to get them to polling stations in rural areas, as Sierra Leone's high court this week upheld a ban on private vehicles circulating on election day, citing national security.
The SLPP has refused to sign a memorandum agreeing to the move, saying it could disenfranchise voters, but Bio told crowds at a final rally on Monday he was "ready for a peaceful election".
The issue of corruption has dominated the campaign, as Bio is accused of stealing $18 million while heading a junta government in 1996 and Kamara is nicknamed "Mr 10 percent" for allegedly skimming his own fee off government contracts.
Meanwhile, outgoing president Koroma's increasing reliance on China for infrastructure, including a new airport and adjoining toll road, have raised concerns Beijing is seeking to keep the APC in power.
"Chinese companies and political officials have bled into the current electoral cycle, shaping public discourse, as well as long-term economic and political decisions," noted the IGR report.
Voter freebies and funding for campaign materials could "potentially influence the voting public" in the APC's favour, it added.